Gene action and combining ability for agronomic traits and biotic stress tolerance in rice

Transcription

1 Gene action and combining ability for agronomic traits and biotic stress tolerance in rice R.A. El-Namaky, 1* S.E.M. Sedeek, 2 S.A.A. Hammoud, 2 B. Manneh 1 and R.A.S. El-Shafey 2 1 Africa Rice Center (AfricaRice), Sahel Station, B.P. 96, Saint Louis, Senegal; 2 Rice Research and Training Center, Sakha 33717, Kafr El-Sheikh, Egypt. Abstract Egypt has the world s highest rice (Oryza sativa L.) productivity, yet yield is constrained by biotic stresses, which are being targeted by breeders. Five parents and their 10 hybrids were used to study gene action, combining ability and heterosis for certain agronomic traits and biotic stresses. Giza177 and M101 rice varieties were resistant to rice blast, while GZ6214 and M202 were resistant to stem borer and M202 to white-tip nematode. General combining ability (GCA) and specific combining ability (SCA) were highly significant for all studied traits. M202 gave highly significant and negative estimates of GCA effects desirable for plant height, vegetative, reproductive and days to. Significant and highly significant negative estimates of SCA effects were found for plant height, vegetative and days to. The best crosses for yield and its components were Giza177 GZ6214, Giza177 M201, Giza177 M202, GZ6214 M201 and GZ6214 M202. In relation to stem borer infestation, crosses M101 M201, M101 M202 and Giza177 GZ6214 gave highly significant and negative estimates (desirable) of SCA. For blast reaction, stem borer infestation and white-tip nematode, two hybrid combinations Giza177 GZ6214 and GZ6214 M201 recorded highly significant negative desirable heterosis and showed highly significant negative SCA effects. M202 was a good source of resistance to white-tip nematode, with all crosses with this cultivar having low levels of infection. Introduction Rice (Oryza sativa L.) is one of the world s most important crops and is the staple food for nearly half the global population (FAO, 2004). In Egypt, where rice is considered the second most important cereal crop after wheat (Bastawisi et al., 2006) and also constitutes one of the country s main agricultural exports, the cultivated area under rice was 0.7 million ha in 2006 with an average yield of 9.84 tonnes/ha the highest productivity in the world (RRTC, 2006). Despite this high average yield, biotic stresses such as blast, stem borers and white-tip nematode constrain rice production in Egypt. Blast disease affects rice production in all rice-growing regions and it can reduce annual rice production by about 5% in normal (mildly-affected) seasons. In epidemic seasons, yield losses may reach as high as 30 50% (Sehly et al., 2002; El-Shafey, 2007). The most cost-effective and preferred means for resource-poor farmers to manage rice blast is the deployment of high-yielding resistant cultivars, but insufficient durability of monogenic blast resistance is a serious problem, especially in upland rice and temperate irrigated rice. Several blastresistant varieties have been released by rice breeding programs and adopted by farmers only to lose their resistance within a few years because of adaptation by the blast pathogen. The loss of resistance has been striking and well documented (Kiyosawa, 1982; Koizumi, 2007). The variable nature of the pathogen often leads to breakdown of host resistance and consequent widespread epidemics. Thus, breeding for durable blast resistance is one of the major challenges faced by rice breeders (Ou, 1985). A high degree of race shifting and changes in prevalence of specific races of blast pathogen resulted in the highly susceptible old rice cultivars Giza159 and Reiho appearing to be resistant and escaping from the disease in some locations in Egypt in the 2005 season. In addition, the cultivars Sakha 101 and Sakha 104 also appeared to be resistant from 1994 to 2002, except for when Sakha 104 was infected in one or all monitored locations with a blast score of 2 4. From 2003 and 2004 onwards, this resistance was broken down in certain locations and these two cultivars became completely susceptible from 2005 to 2007 due to the appearance of specific virulent races of blast: IB-45 specific to Sakha 104, and IG-1 was specific to Sakha 101. This race shifting coincided with an extension of the cultivated areas of both cultivars to 75% of the total rice area in Egypt (El-Shafey, 2002; Sehly et al., 2008). The extensive variability of the blast pathogen means that breeding for greater cultivar diversity must induce changes in the genetic background of promising lines through the introduction of a new resistance genes. Giza177 proved to be a good source of blast resistance, having remained resistant since its release in 1995 (Sehly et al., 2008). White-tip disease of rice leaves, caused by the leaf nematode Aphelenchoides besseyi Christie, is widespread and present in nearly all rice ecosystems worldwide (Ou, 1985), and has recently been found in Egypt where the response of rice cultivars has been significantly different in terms of infection level and yield losses. Older rice cultivars Giza171 and Reiho, and some newer cultivars, suffered extensive losses of up to 47%. Giza178, Giza182, H1, H2, Giza195 and Giza176 are resistant, Sakha101 and Giza177 are moderately * Corresponding author ( R.Elnamaky@cgiar.org). Second Africa Rice Congress, Bamako, Mali, March 2010: Innovation and Partnerships to Realize Africa s Rice Potential 1.3.1

2 susceptible, and Giza171 and Reiho highly susceptible (Abdel-Hadi et al., 2005; El-Shafey, 2007). Some other varieties, such as M201 and M202 originating from the USA, are also resistant to white-tip. Our investigation studied (1) the inheritance of resistance to rice blast, stem borer infestation and white-tip nematode disease, and (2) the genetic behavior of different growth s of selected genotypes and their hybrid combinations that differed mainly in their growth duration. Materials and methods The research was carried out at the Experimental Farm of the Rice Research and Training Center (RRTC), Sakha, Kafr El-Sheikh, Egypt during the rice seasons in 2008 and Five rice varieties Giza177, GZ6214 (Egyptian rice varieties, resistant to blast), M101, M201 and M202 (originating from the USA) were grown at three sowing dates in the 2008 season with 15-day intervals to allow for differences in their dates, and a half-diallel crossing was carried out among them (without reciprocals). Each variety in a replication was represented by three rows 20 cm apart and with 25 plants in each row. Bulk emasculation was conducted using the hot-water technique of Jodon (1938) as modified by Butany (1961). Ten crosses were made and the hybrid seeds were grown in the 2009 rice season; these F 1 plants were transplanted individually after 30 days at a spacing of cm. The experimental plots were grown in a randomized complete block design (RCBD) with three replications. Plot samples were taken at 7-day intervals to determine panicle-initiation. Plant height, ear-bearing tillers (EBT), 1000-grain weight, number of filled grains/panicle and grain yield/plant were measured at harvest. Total chlorophyll in the flag-leaf was recorded at using a chlorophyll meter (5 SPAD-502, Minolta Camera Co. Ltd, Japan). primordium initiation character (3 mm approximately) was recorded by dissecting the main culm of five plants randomly selected from each variety per replication. Blast reaction was recorded according to the standard evaluation system using a scale of 0 9 (IRRI, 1996). White-tip nematode infection The resistance of different varieties was evaluated according to infection percentage: <1% resistant 1 30% moderately susceptible >30 60% susceptible >60% highly susceptible. To estimate the resistance of rice varieties, all rice hills were examined to record the infected hills and calculate the infection percentage using the following formula: Percentage of infection = No. infected hills Total no. rice hills 100 Stem borer evaluation Parents and F 1 offspring were evaluated for stem borer infestation. The reaction of evaluated genotypes was classified into five categories according to the standard evaluation of the Rice Research and Training Center (RRTC, 2006), Sakha, Egypt: < 3% whiteheads (WH) resistant (R) 3 6% WH moderately resistant (MR) 6 9% WH moderately susceptible (MS) 9 12% WH susceptible (S) > 12% WH highly susceptible (HS). Statistical analysis The statistical analysis for estimation of combining ability was done using method 2, model 1 of Griffing (1956). Results and discussion Physiological traits Mean performance Mean performance of all physiological traits for five parents and their crosses are presented (Table 1). The data indicate that all studied traits had a wide range of variability, reflected in the variation among parents and their crosses. The crosses GZ6214 M101 and M201 M202 gave the highest values for flag-leaf area among parents and crosses (45.8 and cm 2, respectively). Crosses M201 M202, M101 M202, Giza Second Africa Rice Congress, Bamako, Mali, March 2010: Innovation and Partnerships to Realize Africa s Rice Potential

3 Table 1. Mean performance of parents and their crosses for physiological traits Genotype Flag-leaf area (cm) Chlorophyll (SPAD) Plant height (cm) Vegetative (days) (days) (cm) Giza GZ M M M Giza GZ6214 Giza177 M Giza177 M Giza177 M GZ6214 M GZ6214 M GZ6214 M M101 M M101 M M201 M LSD at LSD at M101, GZ6214 M101 and M101 M201, and the parent M201 exhibited highest values of chlorophyll (54.33, 52.33, and SPAD, respectively). For plant height, the hybrid combination M201 M202 recorded the shortest plants (69 cm), while the parents and other hybrid combinations ranged between 94 and 124 cm. With regard to vegetative, the parents M101 and M202 and the hybrid combinations GZ6214 M101, Giza 177 M101 and M201 M202 recorded the fewest days to maximum tillering (60, 61, 62 and 63 days, respectively). Meanwhile, M201 and GZ6214 M202 had shortest reporductive (19.0 days). In terms of days to, M202 and M101 were earlest among the parents and crosses (81 and 83.88, respectively). GZ6214 M101 and M101 M201 exhibited the longest panicles (26.0 and 25.0 cm, respectively). Analysis of combining ability Estimates of both general (GCA) and specific combining ability (SCA) variance for physiological traits are presented (Table 2). Both GCA and SCA variances were highly significant for all physiological traits except chlorophyll, indicating the importance of both additive and non-additive genetic variance in determining the inheritance of the studied traits. The relative importance of each variance was determined using the GCA/SCA ratio; the GCA/SCA variances were greater than unity for all studied traits except panicle, suggesting greater importance of additive genetic variance in the inheritance of these traits. Therefore, it could be concluded that selection procedures based on the accumulation of additive effects would be successful in improving these traits. These findings agree with those of Hammoud (1996, 2004), Ammar (1997), El-Malky (1997), Abd El-Aty (2001), El-Refaee (2002), El-Mowafi and Abou Shousha (2003), Sedeek et al. (2007) and Hammoud et al. (2008a). Table 2. Analysis variance and mean square for physiological traits Source of variance d.f. Flag-leaf area Chlorophyll Plant height Vegetative Stage Replications ** 40.07ns 2.96ns 0.16ns 2.22ns 2.29ns 2.32ns Genotypes ** * ** ** 39.26** ** 17.53** Parents ** ns ** ** 49.83** ** 4.10* Crosses ** 64.67** ** ** 37.89** ** 22.04** P vs F ** * ** ** 9.34** ** 30.63** Error GCA ** 37.45ns ** ** 17.00** ** 5.58** SCA ** 10.91ns 69.09** 77.58** 11.52** 51.15** 5.95** Error GCA/SCA *, **, significant at 5% and 1% level, respectively; ns, not significant. Second Africa Rice Congress, Bamako, Mali, March 2010: Innovation and Partnerships to Realize Africa s Rice Potential 1.3.3

4 General combining ability effect Estimates of the GCA effects of individual parental lines for physiological traits are given in Table 3. Highly significant and positive effects of GCA for flag-leaf area, chlorophyll and panicle are perferred for improvement of these traits. While highly significant and negative values for plant height, vegetative phase, reproductive phase and days to are desirable for improvement of these traits in breeding programs since breeders target low mean values. Table 3. Estimation of general combining ability effect for physiological traits Parent Flag-leaf area Chlorophyll Plant height Vegetative Stage Giza ** 1.25ns 1.05** 3.04** 0.41** 2.60** 0.33** GZ ** 3.48** 4.62** 4.56** 1.11** 5.65** 0.97** M ** 1.83* 11.14** 6.87** 2.07** 4.83** 1.46** M ** 1.78* 2.81** 1.13** ** 0.07ns M ** 1.11ns 4.76** 1.87** 1.08** 2.97** 0.09ns LSD at LSD at *, **, significant at 5% and 1% level, respectively; ns, not significant. For flag-leaf area and chlorophyll, varieties M101 and M201 showed highly significant and positive GCA effects, indicating that these varieties could be used as good combiners for improvement of these traits. In relation to plant height, vegetative phase, reproductive phase and days to, M202 gave highly significant and negative GCA effects. The negative values of GCA effects for these traits are required from a breeding perspective since they refer to short stature plant types and earliness. Specific combining ability effect Estimates of SCA effects are given in Table 4. The hybrid combination GZ6214 M101 exhibited highly significant and posstive estimates of SCA for flag-leaf area, chlorophyll and panical, so this hybrid combination may be useful in exploitating heterosis due to their desirable increase in these traits. For plant height, the hybrid combinations M101 M201 and Giza177 GZ6214 gave highly significant and negative values SCA effect. In relation vegetative phase and days to, the crosses Giza177 M101, M201 M202 and GZ6214 M101 gave highly significant and negative values of SCA effects. These crosses could be used in rice breeding programs due to their desirable stature and earliness. Table 4. Estimates of specific combining ability effect for physiological traits Cross Flagleaf area Chlorophyll Plant height Vegetative Stage Giza177 GZ ** 0.75ns 6.32** 4.56** 3.02** 1.51** 3.00** Giza177 M ** 3.27ns 1.41** 6.02** 4.03** 2.02** 0.57** Giza177 M ** 0.01ns 11.87** 8.32** 0.54** 7.60** 2.43** Giza177 M ** 2.34ns 9.83** 4.98** 1.17** 6.46** 1.29** GZ6214 M ** 5.17** 11.59** 7.54** 2.51** 4.73** 4.21** GZ6214 M ** 3.78** 4.46** 7.46** 2.73** 4.56** 0.26ns GZ6214 M ** 2.12ns 1.51** 13.46** 4.35** 9.08** 1.10** M101 M ** 0.09ns 7.44** 5.89** 0.65** 6.37** 2.31** M101 M ** 1.91ns 9.27** 3.89** 1.03** 4.89** 0.67** M201 M ** 3.96** 2.32** 8.11** 4.46** 3.83** 2.14** LSD at LSD at ** significant at 1% level; ns, not significant. Yield and its components Mean performance The mean performance of yield and its components and some biotic stress traits for parents and their F 1 s are presented in Table 5. For nunber of panicles/plant, and grain yield/plant, hybrid combination M101 M Second Africa Rice Congress, Bamako, Mali, March 2010: Innovation and Partnerships to Realize Africa s Rice Potential

5 recorded the highest values (26.0 panicles and g). Concerning number of filled grains per panicle, the hybrid combination Giza177 M202 gave the highest value (206). The hybrid combinations GZ6214 M101 and Giza177 M101 and parent M101 had highest values for 1000-grain weight. All the parents and crosses were resistance to blast, except for parents M201and M202 and cross M201 M202. These results indicate that all the crosses of resistant resistant and resistant susceptible were resistant, while the cross susceptible susceptible was susceptible. Thses indicate that resistance to blast was dominant and susceptibility to blast recessive in this study. For stem borer, the hybrid combinations Giza177 GZ6214, Giza177 M202, M201 M202 and Giza177 M201 were resistant. However, the parent M101 and the crosses Giza177 M101 and GZ6214 M101 were higly suscepible to stem borer. For white-tip nematode, all the parents were highly susibtable except M202, which was resistance (Table 5). However, all the crosses were resistant except Giza177 M201, Giza177 M202, Giza177 GZ6214 and GZ6214 M201, which were moderately resistant. Table 5. Mean performance of parents and their crosses for agronomic traits and biotic stress Genotype No. panicles/ plant No. filled grains/ panicle 1000-grain weight (g) Grain yield/plant (g) Blast reaction (0 9) Stem borer (%) White-tip nematode (%) Giza GZ M M M Giza177 GZ Giza177 M Giza177 M Giza177 M GZ6214 M GZ6214 M GZ6214 M M101 M M101 M M201 M LSD at LSD at Analysis of combining ability Highly significant differences among genotypes (parents and their F 1 s) for yield and its components, blast, stem borer and white-tip nematode resistance indicate a wide range of genetic variation among the parents used in this study (Table 6). Both GCA and SCA variances were highly significant for yield and its components, blast, stem borer and white-tip nematode resistance, indicating the importance of both additive and non-additive genetic variance in the inheritance of the traits studied. GCA/SCA ratio was used to clarify the nature of genetic variance involved. GCA/SCA ratios were greater than unity for 1000-grain weight, blast and stem borer resistance, indicating that additive and additive additive types of gene action were more important in the inheritance of these traits than non-additive types. It could therefore be concluded that selection procedures based on the accumulation of additive effects would be successful in improving these traits. However, GCA/SCA ratios were lower than unity for number of panicles/plant, number of filled grains/panicle, grain yield/plant and white-tip nematode resistance, indicating that non-additive genetic variance (dominance or epitasis) was more important in the inheritance of these traits. This concurs with the findings of Bansal et al. (2000) and Sharma and Mani (2001), who report the importance of non-additive genetic variance in inheritance of yield and its components. General combining ability effect Estimates of the GCA effects of individual parental lines for agronomic traits and biotic stress are given in Table 7. Highly significant and positive GCA for number of panicles/plant, number of filled grains/panicle, 1000-grain weight and grain yield/plant are desirable. While highly significant and negative values for blast, stem borer and white-tip nematode resistance are desirable for improvement of these traits in breeding programs since breeders target low mean values. Second Africa Rice Congress, Bamako, Mali, March 2010: Innovation and Partnerships to Realize Africa s Rice Potential 1.3.5

6 Table 6. Analysis variance and mean square estimates for agronomic traits and biotic stress Source of variance d.f. No. panicles/ plant No. filled grains/ panicle grain weight Grain yield/plant Blast reaction Stem borer White-tip nematode Replications ns 31.40ns 0.13ns 3.76ns 0.42ns 0.35ns 1.32ns Genotypes ** ** 35.69** ** 12.75** ** ** Parents * ** 32.33** ** 19.57** ** ** Crosses ** ** 40.35** ** 6.39** ** 31.36** P vs. F ** ** 7.11** ** 42.71** ** ** Error GCA ** ** 30.74** ** 8.06** ** ** SCA ** ** 4.36** ** 2.73** 42.35** ** Error GCA/SCA *, **, significant at 5% and 1% level, respectively; ns, not significant. Table 7. Estimates of general combining ability effect for agronomic traits and biotic stress Source of variance No. panicles/ plant No. filled grains/ panicle 1000-grain weight Grain yield/plant Blast reaction Stem borer White-tip nematode Giza ** 13.48** 1.05** 3.41** 0.90** 0.22** 5.83** GZ * 4.90** 0.53** 5.84** 0.57** 2.48** 1.23** M ** 3.62** 2.65** 1.79** 0.86** 9.01** 3.61** M ** 9.67** 2.45** 2.54** 1.14** 2.78** 2.32** M ** 2.52** 1.78** 8.50** 1.19** 3.53** 13.00* LSD at LSD at *, **: significant at 5% and 1% level, respectively Giza177 and M101 showed highly significant and positive estimates of GCA effects for number of filled grains/panicle, 1000-grain weight and grain yield/plant, indicating that these varieties could be used in breeding programs as good combiners for these traits. Along with GZ6214, Giza177 also appeared to be a good parental combiner in rice crosses for blast and stem borer resistance, having exhibited highly significant and negative estimates of GCA effects for these traits. Regarding white-tip nematode, M202 gave significant and negative values of GCA effects, indicating that this rice variety could be used as a good combiner for improving resistance to white-tip nematode in Egyptian rice varieties through a crossing program to transfer the genes responsible for resistance from M202. Specific combining ability effect Estimates of SCA effects for F 1 crosses in relation to agronomic traits and biotic stress are presented in Table 8. For number of panicles/plant, M101 M201, M201 M202 and Giza177 M202 gave highly signifacant and positive SCA effects. Giza177 M202, Giza177 M201 and GZ6214 M101 showed highly significant and posititve estimates of number of filled grains/panicale. The cross Giza177 M201 gave highly significant and positive estimate of SCA effects for 1000-grain; as did Giza177 M202, GZ2614 M101, Giza177 M202 and Giza177 M101 for grain yield/plant. These crosses could be used in hybrid rice breeding programs. For blast resistance, six crosses exhibited highly significant and negative values of SCA; the best crosses were GZ6214 M202, GZ6214 M201, M101 M201 and Giza177 M202, indicating that these crosses could be used in breeding programs to improve this trait. A further set of six crosses showed highly significant and negative SCA effects for stem borer resistance. The best combinations giving the highest values were M101 M201, M101 M202 and Giza177 GZ6214, indicating that these crosses could be used in breeding programs, and their parents used as good donors for resistance genes to counteract stem borer. All crosses gave highly significant and negative estimates of SCA effects for white-tip nematode. The best crosses were Giza177 M101, M101 M201, Giza177 GZ6214 and GZ6214 M101, indicating that these could be used for crossing to improve resistance to this nematode Second Africa Rice Congress, Bamako, Mali, March 2010: Innovation and Partnerships to Realize Africa s Rice Potential

7 Table 8. Estimates of specific combining ability effect for agronomic traits and biotic stress Cross No. panicles/ plant No. filled grains/panicle 1000-grain weight Grain yield/plant Blast reaction Stem borer White-tip nematode Giza177 GZ ** 29.24** 2.01** 5.06** 0.25ns 3.27** 20.96** Giza177 M ns 17.90** 0.54** 5.89** 0.87** 11.24** 25.50** Giza177 M ** 47.19** 2.43** 13.44** 1.46** 2.24** 14.38** Giza177 M ** 52.71** 1.17** 27.06** 1.51** 2.22** 4.06** GZ6214 M ns 43.29** 1.96** 16.35** 0.21ns 1.54** 20.93** GZ6214 M ** 8.24** 0.95** 5.35** 1.79** 0.38** 18.45** GZ6214 M ** 8.76** 1.29** 14.63** 1.84** 2.40** 4.29** M101 M ** 23.38** 0.87** 27.40** 1.51** 10.54** 22.02** M101 M ** 35.43** 0.06ns 11.32** 1.22** 8.92** 6.67** M201 M ** 34.81** 4.33** 16.98** 1.11** 0.83** 5.41** LSD at LSD at ** significant at 1% level; ns, not significant. Heterosis Useful heteroses expressed as the percentage deviation of F 1 mean values from their respective better parent estimates for physiological traits, yield and yield components, together with some for biotic stress, are presented in Tables 9 and 10. Significant positive heterosis relative to better parent values would be of interest for flagleaf area, chlorophyll, panicle, number of panicles/plant, number of filled grains/panicle, grain weight and grain yield/plant. Breeders would also find it useful to have significant negative heterosis relative to better parent values for plant height, vegetative, reproductive, days to, and reactions to blast, stem borer and white-tip nematode. Significant and highly significant positive estimates of heterosis over better parent for flag-leaf area were recorded for six crosses (Table 9). Moreover, since these heteroses were computed on the basis of SCA, it seems that dominance plays a major role in inheritance of this trait. The best crosses were M201 M202, GZ6214 M101 and Giza177 M202. Highly significant negative heterosis for plant height and reproductive was exhibited by the cross GZ6214 M202. Of the four crosses showing highly significant and positive hererosis for panicle, the best crosses were GZ6214 M101, M101 M201 and Giza177 M201. Table 9. Estimates of heterosis over better-parent for physiological traits Cross Flag-leaf area Chlorophyll Plant height Vegetative Giza177 GZ ** 6.46ns 1.03ns 16.66** 2.77** 12.10** 15.00** Giza177 M ns 11.59ns 15.51** 3.33** 34.25** 9.20** 9.52** Giza177 M ** 5.88ns 23.40** 25.26** 8.42** 20.69** 16.65** Giza177 M ** 8.16ns 14.29** 27.86** 15.00** 25.10** 3.94ns GZ6214 M ** 10.87ns 27.84** 3.33** 24.46** 9.60** 23.81** GZ6214 M ** 17.65ns 0.00ns 26.3** 5.26** 20.69** 0.00ns GZ6214 M ** 12.24ns 2.06** 44.26** 5.00** 32.10** 0.00ns M101 M * 0.00ns 29.43** 20.00** 27.89** 15.60** 19.05** M101 M ** 6.80ns 5.10** 11.66** 26.5** 13.99** 3.14ns M201 M ** 6.53ns 2.13** 3.27** 31.57** 8.64** 10.92** LSD at LSD at *, **: significant at 5% and 1% level, respectively; ns: not significant. In respect of number of panicles/plant, number of filled grains/panicle and grain yield/plant, the crosses Giza177 M201, Giza177 M202, GZ6214 M201 and M101 M201 exhibited highly significant positive heterosis and recorded highly significant and positive SCA effects, indicating that dominance plays a major role in the inheritance of these traits, which appears as high heterosis over the better parent. For blast reaction, three hybrid combinations recorded highly significant negative heterosis and showed highly significant negative SCA effects, indicating that dominance plays a major role in the inheritance of this trait. The best crosses were Giza177 GZ6214, GZ6214 M201 and GZ6214 M202. These crosses could be used in a hybridization breeding program for improving this trait. Second Africa Rice Congress, Bamako, Mali, March 2010: Innovation and Partnerships to Realize Africa s Rice Potential 1.3.7

8 Table 10. Estimates of heterosis over better-parent for agronomic traits and biotic stress Source of variance No. panicles/ plant No. filled grains/panicle grain weight Grain yield/plant Blast reaction Stem borer White-tip nematode Giza177 GZ ** 2.66ns 5.23** 50.21** 20.36** 50.00** 96.00** Giza177 M ns 41.86** 1.95** 19.56** 0.00ns ** 99.60** Giza177 M ** 54.66** 0.00ns 64.31** 20.36ns 52.50** 80.40** Giza177 M ** 45.41** 2.14** 82.15** 20.36ns 58.00** ** GZ6214 M ns 47.46** 4.89** 18.02** 20.36ns ** 99.80** GZ 6214 M ** 16.24** 3.44** 37.98** 55.67** 23.80** 98.00** GZ6214 M ** 1.41ns 0.26ns 45.06** 55.67** 7.10** 0.00 M101 M ** 27.74** 8.37** 78.91** 20.36ns 54.20** 99.80** M101 M ** 23.77** 9.22** 18.26** 0.00ns 8.00** 0.00 M201 M ** 32.71** 24.40** 23.33** 10.04ns 48.00** 0.00 LSD at LSD at ** significant at 1% level; ns, not significant. Likewise, the major role of dominance in the inheritance of resistance traits for stem borer and white-tip nematode was identified through four crosses, Giza177 GZ6214, Giza177 M201, GZ6214 M201 and M101 M201, which showed good SCA effects. Genetic components of variation as defined by Hayman (1954) The data obtained gave more information about the genetic behaviour of the agronomic traits under investigation. The mean values of each cross were used to estimate the different genetic components of variation D, H1, H2, H and F as defined by Hayman (1954). It is clear that the additive component (D) was highly significant for flag-leaf area, chlorophyll, plant height, reproductive, days to, 1000-grain weight, and reaction to blast, stem borer and white-tip nematode (Tables 11 and 12). Meanwhile, dominance genetic components (H1 and H2) were significant and highly significant for all traits studied. H1 and H2 were greater in their magnitude than the corresponding additive genetic variation (D) for all traits under investigation. It may be concluded that the dominance genetic variation had a greater role in inheritance for all traits studied. However, according to the combining ability analysis the additive genetic variance was of greater importance in the inheritance of most traits studied. This contradiction between the two different approaches could be attributed to the presence of non-allelic interactions: Mather and Jinks (1982) state that the additive genetic variation (D) would be affected by the presence of non-allelic interaction. The positive F values were significant and highly significant for reproductive and blast reaction, respictively. Irrespective of whether dominant alleles are increasing or decreasing in their effect on reproductive and blast reaction, the positive F values showed that there are more dominant alleles present in the parental lines than recessive alleles, where the estimated values in other traits were negative. The increase of genes either dominant or recessive that control these traits was not consistent for the different traits, suggesting that the non-additive gene action was susceptible to environmental change, and that the degree of dominant or recessive inheritance for each trait may be determined by the growing conditions (Mather and Jinks, 1982). The overall dominance variance as the algebraic sum over all heterozygous loci in all crosses (H2) was significant and highly significant for flag-leaf area, plant height, vegetative, days to, panicle, number of panicles/plant, grain yield/plant, and reaction to blast and white-tip nematode, indicating the prevalence of dominance effect over all loci in all crosses. However, the estimates of H2 were not significant for other traits, which indicated that an absence of dominance effect over all loci in the heterozygous state in these traits. This could be due to the presence of a considerable amount of canceling dominance effects in the parental varieties. Similar results are reported by Niranjana et al. (1999), Tripathi et al. (1999) and Tiwari et al. (1999). The environmental components (E) were non-significant but nevertheless different in their magnitude for the traits studied, indicating that these traits were affected to differing degrees by the environmental conditions. The average degree of dominance (H/D) 1/2 in the F 1 generation was greater than unity for all traits studied, indicating overdominance for these traits. When positive and negative genes are equally distributed in the parental varieties, the proportion H2/4H1 is expected to be The estimates of H2/4H1 were lower than 0.25 for all traits studied, indicating that the positive and negative alleles were not equally distributed among the parents. The proportion of dominant to recessive alleles in the parents was greater than unity for flag-leaf area, reproductive, days to, number of panicles/plant, number of filled grains/panicle, and reactions to Second Africa Rice Congress, Bamako, Mali, March 2010: Innovation and Partnerships to Realize Africa s Rice Potential

9 blast, stem borer and white-tip nematode, indicating a greater proportion of dominant alleles than recessive alleles for these traits. This also confirmed the existence of more dominant than recessive genes in the parental varieties, as previously discussed. Concerning the positive values for the F parameter, the excess of dominant genes over recessive genes and vice versa suggested that the excess of genes, whether dominant or recessive, controlling these traits was not consistent under the different conditions. The degree of dominance or recessivity may be determined by the growing conditions. This finding confirms the results previously discussed concerning the positive or negative values of the F parameter. Similar results were previously obtained by Hammoud (1996, 2004), Salem (1997), Surek and Korkut (1998), El-Abd and Abdallah (2002) and El-Refaee (2002). Heritability Heritability estimates in the broad and narrow sense for agronomic traits are also presented in Tables 11 and 12. High heritability values in the broad sense (Hb) were detected for all traits, indicating that the additive and nonadditive genetic variance was of greater importance in the inheritance of these traits. High estimates (>50%) of heritability in the narrow sense (Hn) were detected for chlorophyll, plant height, 1000-grain weight and stem borer infection rate, while moderate Hn was found for vegetative, days to and blast reaction. Low estimates of Hn were obtained for flag-leaf area, reproductive, panicle, number of panicles/plant, number of filled grains/panicle, grain yield/plant and white-tip nematode infestation. It could be concluded that the selection procedures which are known to be effective in shifting gene frequency, when both additive and non-additive genetic variation are involved, would be successful in improving most of the traits under examination. Similar results are reported by Sedeek et al. (2007), El-Wahsh and Hammoud (2007) and Hammoud et al. (2008b). Conclusion This study concluded that M101 rice variety could be considered a good combiner for improving flag-leaf area, chlorophyll and panicle, while Giza177 and M101 proved to be excellent combiners for number of filled grains/panicle, 1000-grain weight and grain yield/plant. M202 was identified as best combiner for stem borer and white-tip nematode resistances. This study also indicated that additive and additive additive types of gene action were more important in the inheritance of blast and stem borer resistances. However, non-additive genetic variance (dominance or epitasis) was more important in the inheritance of grain yield and white-tip nematode resistence. Also, a greater proportion of dominant alleles than recessive alleles were observed for flag-leaf area, reproductive, days to, number of panicles/plant, number of filled grains/panicle, and reactions to blast, stem borer and white-tip nematode. References Abd El-Aty MSM Heterosis and combining ability for grain yield and some related bcharacters in rice (Oryza sativa L.). Journal of Agricultural Research (Tanta University) 27(3): Abdel-Hadi MA, El-Shafeey EI, Tadros MS and Soliman MH Occurrence, distribution and epidemics of white-tip nematode, Aphelenchoides besseyi on rice plants in Egypt. Mansoura University Journal of Agricultural Science 30(2): Ammar MHM Breeding studies on rice through anther culture. MSc Thesis. Agronomy Department, Faculty of Agriculture, Minufiya University, Shibin El-Kom, Egypt. Bansal UK, Saini RG and Rani NS Heterosis and combining ability for yield, its components and quality traits in some scented rices (Oryza sativa L.). Tropical Agriculture 77(3): Bastawisi AO, El-Mowafi HF, Maximos MA and Sobaa MF Hybrid rice production technology in Egypt. In: Proceeding: Workshop on Rice Integrated Crop Management Systems for Food Security in the Near East Countries, Alexandria, Egypt, July Food and Agriculture Organization of the United Nations Regional Office for the Near East, Cairo. Butany WT Mass emasculation in rice. International Rice Commission Newsletter 9: El-Abd AB and Abdallah AA Genetical studies on yield and its related characters in rice (Oryza sativa L.). Proceedings of the 2nd conference of the Sustainable Agricultural Fayom branch, Cairo University, (10): El-Malky MM Studies on some genetic characters in rice using tissue culture techniques. MSc Thesis. Genetics Department, Faculty of Agriculture, Minufiya University, Shibin El-Kom, Egypt. El-Mowafi HF and Abou Shousha AA Combining ability and heterosis analysis of diverse CMS lines in hybrid rice. Journal of Agricultural Research (Tanta University) 29(1): El-Rafaee YZA Genetical and biochemical studies on heterosis and combining ability in rice. MSc Thesis. Genetics Department, Faculty of Agriculture, Kafrelsheikh, Tanta University, Egypt. El-Shafey RAS Studies on Pyricularia oryzae the causal organism of rice blast disease and its control. MSc Thesis. Faculty of Agriculture, Minufiya University, Egypt. Second Africa Rice Congress, Bamako, Mali, March 2010: Innovation and Partnerships to Realize Africa s Rice Potential 1.3.9

10 Table 11. Components of variance and other statistics for some physiological traits in the F 1 generation Source of variance Flag-leaf area Chlorophyll Plant height Vegetative D ± 8.37** ± 3.34** ± 12.47** ± ± 3.08** ± 5.78** 1.09 ± 2.09 F 32.17± ± ± ± ± 9.50 * 3.35 ± ± 5.71 H ± 22.59** ± 9.03** ± 33.67** ± 62.33** ± 10.27** ± 15.61** ± 6.17** H ± 2049** ± 8.19** ± 30.54** ± 56.53** ± 9.32** ± 14.15** ± 5.06** h ± 13.84** 6.18 ± ± 20.62** ± 38.17** 2.21 ± ± 9.56** 7.66 ± 3.78* E 0.39 ± 3.42ns 0.49 ± ± ± ± ± ± 0.93 (H1/D) 1/ H2/4H KD/KR R Hb Hn *, ** Significant at 0.05 and 0.01 levels of probability, respectively. Table 12. Components of variance and other statistics for some agronomic traits and biotic stresses in the F 1 generation Source of variance No. No. filled 1000-grain Grain yield/plant Blast reaction Stem borer White-tip nematode panicles/plant grains/panicle weight D 1.23 ± ± ± 2.49** ± ± 0.23** ± 29.86** ± ** F 0.96 ± ± ± ± ± 0.56** ± ± H ± 5.97** ± ** ± 6.72** ± ** 8.45 ± 0.61** ± 80.64* ± ** H ± 5.41** ± ** ± 6.10** ± ** 8.10 ± 0.55** ± 73.14* ± ** h ± 3.65** ± ± ± ** ± 0.37** ± ± ** E 0.47 ± ± ± ± ± ± ± (H1/D) 1/ H2/4H KD/KR r Hb Hn *, ** Significant at 0.05 and 0.01 levels of probability, respectively Second Africa Rice Congress, Bamako, Mali, March 2010: Innovation and Partnerships to Realize Africa s Rice Potential

11 El-Shafey RAS Biological and ecological studies on white-tip nematode in rice with special reference to its control. PhD Thesis. Faculty of Agriculture, Kafrelsheikh University, Egypt. El-Wahsh SM and Hammoud SAA Evaluation of rice promising lines for blast disease resistance and some agronomic characters. Journal of Agricultural Research, Kafrelsheikh University 33(1): FAO The state of food and agriculture Agricultural biotechnology: Meeting the needs of the poor? FAO Agriculture Series No. 35. Food and Agriculture Organization of the United Nations, Rome. Griffing JB Concept of general and specific combining ability in relation to diallel crossing systems. Australian Journal of Biological Sciences 9: Hammoud SAA Breeding studies on some rice characters. MSc Thesis. Agronomy Department, Faculty of Agriculture, Minufiya University, Shibin El-Kom, Egypt. Hammoud SAA Inheritance of some quantitative characters in rice (Oryza sativa L.). PhD Thesis. Agronomy Department, Faculty of Agriculture, Minufiya University, Shibin El-Kom, Egypt. Hammoud SAA, El-Degwy ISM, Sedeek SEM and Zayed BA. 2008a. Line tester analysis for some quantitative traits in rice. p In: Proceedings: The Second Field Crops Conference, Giza, Egypt, October Field Crops Research Institute, Agricultural Research Center, Giza, Egypt. Hammoud SAA, El-Habashy MM, El-Gohary A and Abd El-Latief ASM. 2008b. Combining ability, heterosis and correlation coefficient of some rice genotypes for yield and yield components and stem borer infestation. In: Proceedings: The Second Field Crops Conference, Giza, Egypt, October Field Crops Research Institute, Agricultural Research Center, Giza, Egypt. Hayman BI The analysis of variance of diallel tables. Biometrics 110: IRRI Standard Evaluation System for Rice. International Rice Research Institute, Manila, Philippines. Jodon NE Experiments on artificial hybridization of rice. Journal of the American Society of Agronomy 30: Kiyosawa S Genetic and epidemiological modeling of breakdown of plant disease resistance. Annual Review of Phytopathology 20: Koizumi S Durability of resistance to rice blast disease. p In: Fukuta Y, Vera Cruz CM and Kabayashi N eds. A differential system for blast resistance for stable rice production environment. JIRCAS Working Report No. 53. Japan International Research Center for Agricultural Sciences, Tsukuba, Japan. Mather K and Jinks JL Biometrical Genetics: The Study of Continuous Variation (3rd edn). Chapman and Hall, London. 396 p. Niranjana M, Kulkarni RS, Udaykumar M and Murthy N Genetic variability, heritability and genetic advance for morpho-physiological traits in rice. Oryza 36(2): Ou SH Rice Diseases (2nd edn). CMI, Kew, UK. RRTC (Rice Research and Training Center) Annual Rice National Campaign Report of Rice Program. Field Crops Research, Agricultural Research Center, Ministry of Agriculture, Egypt. Salem KFM Breeding studies on rice (Oryza sativa L.). MSc Thesis. Faculty of Agriculture, Minufiya University, Shibin El-Kom, Egypt. Sedeek SEM, Hammoud SAA, El-Abd AB and Rewainy IOM Generation mean analysis of some agronomic traits, blast disease and stem borer resistance in two rice crosses under two N-levels. Egyptian Journal of Plant Breeding 11: Sehly MR, Osman ZH and Salem EA Rice diseases. p 301. In: Rice in Egypt. Sehly MR, El-Wahsh SM, Badr EAS, El-Malkey MMH, El-Shafey RAS and Aidy IR Evaluation of certain Egyptian rice cultivars to blast disease incidence during fourteen years in Egypt. Mansoura University Journal of Agricultural Science 33(4): Sharma DK and Mani SC Combining ability studies for grain yield and other associated characters in Basmati rice (Oryza sativa L.). Crop Improvement (India) 28(2): Surek H and Korkut KZ Diallel analysis of some quantitative characters in F 1 and F 2 generations in rice (Oryza sativa L.). Egyptian Journal of Agricultural Research 76(2): Tiwari VN, Mishra R and Sarathe ML Selection criteria based on narrow sense heritability in early generation of rice. Agricultural Science Digest 19(1): Tripathi AK, Sinha SK and Bhandarkar S Studies on variability, heritability and genetic advance of semideep water rice. Plant Sciences 12(1): Second Africa Rice Congress, Bamako, Mali, March 2010: Innovation and Partnerships to Realize Africa s Rice Potential