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1 GROWTH AND SEED YIELD COMPONENTS OF INDIAN MUSTARD (BRASSICA JUNCEA L.) AND CANOLA (BRASSICA NAPUS L.) IN A LOW RAINFALL SHORT SEASON MEDITERRANEAN TYPE ENVIRONMENT C. P. Gunasekera 1, L.D. Martin 1, G.H. Walton 2 and K.H.M. Siddique 1 Muresk Institute of Agriculture, Curtin University of Technology, Northam, WA 641 <gunasekp@ses.curtin.edu.au>,<lionel.martin@curtin.edu.au> 2 Agriculture Western Australia, Locked Bag No. 4, Bentley Delivery Center, Bentley 698 <gwalton@agric.wa.gov.au> Center for Legumes in Mediterranean Agriculture, University of Western Australia, Nedlands, WA 697 <ksiddiqu@agric.uwa.edu.au> ABSTRACT The morpho-physiological basis of adaptation and yield improvement of Indian mustard (Brassica juncea L.) was compared to canola (B. napus L.) in the low rainfall cropping region at Merredin, WA (1 o 29 S, 118 o 18 E) during 2 growing season. The effects of genotype, time of sowing and their interaction on phenology, growth, dry matter production, seed yield and yield components were investigated by sowing seven genotypes of Indian mustard and canola at three times. The study demonstrated that short statured and early maturing mustard lines are well adapted to low rainfall, short season Mediterranean type environments at Merredin especially when sown early (mid May). They posses desirable morphological and physiological attributes that enable these lines to perform well in this environment. KEYWORDS Genotype x environment interaction, Radiation Absorption, Leaf Area Index, Canopy Development, Harvest Index INTRODUCTION Adaptation of a crop to low rainfall, short season, Mediterranean environment depends on it s ability to escape or tolerate drought and make efficient use of resources to produce biomass and partition it into seed yield (Loss and Siddique, 1994). Identification and manipulation of relatively simple morphological character(s), which have significant effect on physiological processes determining the yield is one of the practical approaches to improve the yield in this type of environment (Thurling, 1991). A crop with rapid canopy development, early flowering and rapid grain filling is capable of completing its life cycle before terminal drought sets in (Loss and Siddique, 1994). Seed yield is often related to the amount of dry matter accumulated in many crops (Lewis and Thurling, 1994; Mwanamwenge et al., 1997; Siddique et al., 1999) which is in turn directly related to light interception by the canopy. Light interception in an annual crop depends on the rate of leaf canopy development and canopy architecture (Thomson and Siddique, 1997) characterized by morphological variants such as leaf and pod shape and inclination. Production of grater biomass is not effective unless it is partitioned efficiently into the economical yield (Loss and Siddique, 1994). Yield components such as number of pods/plant, number of seeds/pod and seed weight also are important aspects of seed yield in Brassica oil crops (Thurling, 1991). The major objective of this study was to identify morphological and physiological characteristics, which determine the yield and adaptation of mustard and canola in low rainfall cropping regions of Western Australia.

2 MATERIAL AND METHODS A field experiment was conducted in low rainfall cropping region of Western Australia at Merredin (1 o 29 S, 118 o 18 E) in the 2 growing season. Treatments consisted of three times of sowing (16 May, 9 June and June) and seven genotypes (five of Indian mustard and two of canola). Details of experimental design, description of genotypes and trial management is given in Gunasekera et al (21). Two representative mustard genotypes (82 No and JM ) and one representative canola genotype (Oscar) were selected for detailed measurements of biomass production and partitioning, Leaf Area Index (LAI) and the percentage absorption of Photosynthetically Active Radiation (PAR). Plant samples, LAI and PAR measurements were collected every four weeks commencing from six weeks after emergence until physiological maturity. Two 1m 2 quadrats from each plot was harvested at maturity and seed yield, final above ground biomass, harvest Index (HI) were estimated. Yield components were determined using ten median plants harvested from each plot. The reminder of the plot was machine harvested. All measurements were subjected to analysis of variance using Genstat statistical package. RESULTS Canopy development and radiation absorption The effect of genotype and times of sowing on Maximum LAI and PAR absorption was significant (P <.5); however, genotype x times of sowing interaction was not significant. PAR absorption followed the same pattern as LAI (Figure 1). Maximum LAI of three genotypes was not significantly different in early and mid sowings and maximum PAR absorption of three genotypes was not significantly different when sown early. Maximum LAI of JM and Oscar was significantly lower than 82 No when sown late in the season and PAR absorption of Oscar was significantly lower than two mustard lines from mid and late sowings. Maximum LAI and PAR absorption of early mustard line 82 No was not significantly affected by times of sowing (Figure 1). Maximum LAI of mid season mustard line JM and canola variety Oscar was however significantly lower in late sowing than early and mid sowings. Maximum PAR absorption of JM and Oscar were significantly lower in mid and late sowings. Biomass production Maximum above ground biomass production of mustard was significantly higher than canola in all times of sowing (Figure 2). There was no significant difference between 82 No and JM in their maximum above ground biomass production from early and mid sowings and both lines produced significantly higher biomass than Oscar. The mustard line 82 No produced significantly higher biomass than JM and Oscar, even in the late sowing. All three genotypes produced significantly higher above ground biomass when sown early. Maximum biomass production of 82 No and JM from mid and late sowings was not significantly different and that of Oscar was progressively reduced with delayed sowing (Figure 2). Times of sowing had no significant effect on the above ground biomass production at flowering (Table 1), but the effects of genotype and genotype x time of sowing interaction on that were significant (P <.1). Above ground biomass production at final harvest was highest from early sowing and it decreased significantly as sowing was progressively delayed (Table 1). Although there was no difference in biomass production at flowering between mustard and canola, mustard lines produced more biomass at final harvest than canola regardless of the time of sowing.

3 I II III LAI PAR Day of the year Figure 1. LAI and PAR absorption of two mustard [82 N ( ), JM ( )] and canola [Oscar ( )] genotypes sown at three times [Early (I), Mid (II) and late (III)] at Merredin in 2. I II III Bio mass production (g/m2) Day of the year Figure 2. Bio mass production (g/m 2 ) of two mustard [82 N ( ), JM ( )] and canola [Oscar ( )] genotypes sown at three times [Early (I), Mid (II) and late (III)] at Merredin in 2.

4 Table 1. Log e Above ground bio mass production (g/m 2 ) at flowering, final harvest and Harvest Index (%) of seven genotypes of mustard and canola sown at three times at Merredin in 2. Genotype Log e Above ground biomass production at flowering (g/m2) Log e Final above ground biomass production (t/ha) Harvest Index Early Mid Late Mean Early Mid Late Mean Early Mid Late Mean JM JM Muscon NO Monty Oscar Mean LSD (P =.5) TOS =.7 VAR =.5 TOS X VAR = 1.2 VAR / Same levels of TOS = 1.1 TOS =.285 VAR =.164 TOS X VAR =.44 VAR / Same levels of TOS =.28 TOS = 5. VAR = 2.5 TOS X VAR = 5.7 VAR / Same levels of TOS = 4.4 Harvest index and Yield components Harvest index was not affected by time of sowing, but was significantly different between genotypes. Although canola had greater harvest indices than mustard when sown early, this was reversed in the late sowing (Table 1). All mustard lines produced a greater number of pods/ plant than canola. Number of pods/plant was highest from the early sowing. Canola produced significantly higher number of seeds/ pod than mustard and it varied significantly between genotypes. Mean seed weight (g/1 seeds) varied between genotypes (P <.1) but was not significantly affected by times of sowing. Table 2. Yield components of seven genotypes of mustard and canola sown at three times at Merredin in 2. Genotype Pods/ plant Seeds/pod 1 seed weight (g) Early Mid Late Mean Early Mid Late Mean Early Mid Late Mean JM JM Muscon NO Monty Oscar Mean LSD (P =.5) TOS = 1.1 VAR =.88 TOS X VAR = 1.64 VAR / Same levels of TOS = 1.52 TOS = 1.75 VAR = 2. TOS X VAR =.49 VAR / Same levels of TOS =.52 TOS =.28 VAR =.144 TOS X VAR =.279 VAR / Same levels of TOS =.248 DISCUSSION This study demonstrates that short statured and early maturing mustard lines are well adapted to low rainfall, short season Mediterranean environment at Merredin when they are sown early in the season. These lines showed vigorous seedling growth, early stem elongation; rapid ground cover and early flowering under sub optimal temperatures and radiation levels early in the season. Performance of

5 mustard in this environment was better than canola in all times of sowing and it was more apparent in mid and late sowings. Superior performance of mustard in this low rainfall environment even in late sowings confirms its superior adaptation and greater tolerance to water and heat stress than canola. Similar observations on the performance of mustard over canola in water limited environments were reported in several other studies (Kumar et al., 1987, 1994; Lewis and Thurling, 1994; Wright et al., 1996). Early mustard line produced more leaves and branches than canola even in the late sowing and had greater leaf area indices. This in turn allowed the crop to absorb more PAR and to produce significantly greater biomass. Biomass production at flowering was not significantly different between mustard and canola but mustard lines produced significantly greater biomass at final harvest than canola regardless of the time of sowing. Early flowering and longer reproductive phases of mustard lines compared to canola in this environment allowed sufficient time to accumulate greater post anthesis dry matter production before the onset of terminal drought. This resulted in greater biomass production at physiological maturity and eventually to produce significantly higher seed yield than canola. Similarly, an optimal time for the commencement of flowering, which recognizes a balanced pre and post anthesis development, have been identified as important criteria of selecting higher yields in similar environments (Lewis, 1992; Thurling, 1991; Thurling and Vijendra Das, 1979). Moreover, we found that the biomass production at final harvest was highest from early sowing and it decreased significantly with delayed sowing despite the fact that at flowering it was consistent across times of sowing. Late sown crops did not have sufficient period to accumulate post anthesis biomass to support the completion of seed development before the onset of terminal drought in this environment. Accumulation of biomass before flowering alone was not sufficient to support the seed development. As reported in previous studies (Lewis and Thurling, 1994; Richards, 1978; Siddique et al., 1999; Thurling, 1974), we found a strong positive correlation between seed yield and biological yield. ACKNOWLEDGEMENTS Mustard germplasm was kindly supplied by the National Mustard Breeding Program at Horsham, Victoria. We greatly appreciate the technical assistance of Tammi Short and Ruwan Warnakula. REFERENCES Gunasekera, C.P., Martin, L.D., Walton, G.H. and Siddique K.H.M. (21). Indian mustard (Brassica juncea L.) a promising oil seed crop for low rainfall cropping regions of western Australia. In "12th Australian Research Assembly on Brassicas". Kumar, A., Singh, D. P. and Singh, P. (1987). Genotypic variation in the responses of Brassica species to water deficit. Journal of Agricultural Science 19, Kumar, A., Singh, D. P. and Singh, P. (1994). Influence of water stress on photosynthesis, transpiration, water use efficiency and yield of Brassica juncea L. Field Crops Research 7, Lewis, G. (1992). Strategies for improvement of canola yields in a Mediterranean environment. PhD Thesis, University of Western Australia, Perth, Western Australia. Lewis, G. J. and Thurling, N. (1994). Growth, development and yield of three oilseed Brassica species in a water limited environment. Australian Journal of Experimental Agriculture 4, 9-1. Loss, S. P. and Siddique, K. H. M. (1994). Morphological and physiological traits associated with wheat yield increases in Mediterranean environments. Advances in Agronomy 52, Mwanamwenge, J., Siddique, K. H. M. and Sedgley, R. H. (1997). Canopy development and light absorption of grain legume species in a short season Mediterranean type environment. Journal of Agronomy and Crop Science 179, 1-7.

6 Richards, R. A. (1978). Variation between and within species of rapeseed (Brassica campestris and B. napus) in response to drought stress III. Physiological and Physiochemical characters. Australian Journal of Agricultural Research 29, Siddique, K. H. M., Loss, S. P., Regan, K. L. and Jettner, R. L. (1999). Adaptation and seed yield of Cool season grain legumes in Mediterranean environments of South Western Australia. Australian Journal of Agricultural Research 5, Thomson, B. D. and Siddique, K. H. M. (1997). Grain legume species in low rainfall Mediterranean type environments I. Canopy development, radiation interception, and dry matter production. Field Crops Research 54, Thurling, N. (1974). Morphological determinants of yield in rapeseed (Brassica campestris and Brassica napus) I. Growth and Morphological characters. Australian Journal of Agricultural Science 25, Thurling, N. (1991). Application of the ideotype concept in breeding for higher yield in the oilseed Brassicas. Field Crops Research 26, Thurling, N. and Vijendra Das, L. D. (1979). The relationship between pre anthesis development and seed yield of spring rape (Brassica napus L. ). Australian Journal of Agricultural Science 1, Wright, P. R., Morgan, J. M. and Jessop, R. S. (1996). Comparative adaptation of canola (Brassica napus) and Indian mustard (B. juncea) to soil water deficits: Plant water relations and growth. Field crop Research 49,