Department of Plant Breeding and Genetics COLLEGE OF AGRICULTURE VELLAYANI, THI~UV ANANTHAPURAM

Transcription

1 GENETIC ANALYSIS FOR YIELD AND RESISTANCE TO YELLOW VEIN MOSAIC IN OKRA (Abeimosc/Ills esclilelftlts (L.) Moench) P. SINDHUMOLE Thesis submitted in partial fulfilment of the requirement for the degree of Doctor of Philosophy Faculty of Agriculture Kerala Agricultural University, Thrissur 2003 Department of Plant Breeding and Genetics COLLEGE OF AGRICULTURE VELLAYANI, THI~UV ANANTHAPURAM :.':;. I

2 CERTIFICATE Certified that this thesis entitled "Genetic Analysis for Yield and Resistance to Yellow Vein Mosaic in Okra (Ahelllla,""/Ill," e.",'u/entu." (L.) Moench)" is a record of research work done independently by Mrs. P. Sindhumole ( ) under my guidance and supervision and that it has not previously formed the basis for the award of any degree, fellowship or associateship to her. Vellayani, (~ Dr. P. Manju (Chairman, Advisory Committee) Associate Professor Department of Plant Breeding and Genet ics College of Agriculture, Vellayani Thiruvananthapuram.

3 8. ABSTRACT The most dreaded disease affecting okra (A he/f11()schlls esli/ellllls (L.) Moench) is yellow vein mosaic (YVM), which affects at all stages of the crop growth. Being a viral one, the best way to tackle this disease is to use resistant varieties. Thus it is essential to identify the sources of YVI\1 resistance and study the inheritance of resistance to develop high yielding YVM resistant varieties of okra. Hence an investigation was undertaken to reveal the genetic variability and to identify the resistant genotypes in a. collection line x tester of germ plasm, to estimate the combining ability and heterosis by analysis and to assess the inheritance pattern of YVM resistance and yield using generation mean analysis in order to formulate an appropriate breeding programme for improving the economic characters. Okra germplasm consisting of 101 genotypes was evaluated simultaneously for YVM resistance and yield traits as two parall.el field experiments in RBD with two replications during summer Screening for YVM resistance was carried out at four crop stages vi::., 30 DAS, 50 DAS, 70 DAS and final harvest. ANOV A revealed significant variation among genotypes during all the stages except at 30 DAS. Number of susceptible genotypes as well as disease intensity increased gradually from 30 DAS to final harvest. Four genotypes exhibited high resistance to YVM throughout the crop phase. All the genotypes were observed for vector population of white fly and leaf hopper in the morning and evening at 30 DAS, 50 DAS and 70 DAS and they varied significantly for white fly population during all the crop stages whereas for leaf hopper count only at 50 DAS. Morning and evening populations of both vectors at 30 DAS had significant association with disease occurrence during 50 DAS to final harvest. During the evaluation of yield traitsj ANOV A revealed significant variation among the genotypes for the traits vi::., days to first flower, leaf axil bearing first flower, leaf area, pollen sterility, fr-vits plant', average

4 fruit weight, fruit weight planrl (yield), fruit length, fruit girth, ridges fruir I, seeds fruir I, plant duration, crude fibre content, protein content, mucilage content, fruit and shoot borer incidence, YVM incidence (except at 30 DAS). Besides, colour and pubescence of fruits also were scored for each genotype. The maximum values of both phenotypic and genotypic coefficients of variation were noticed for protein content and fruit yield. Most of the traits possessed high heritability especially fruits planrl, fruit yield and ridges fruir'. High genetic advance (% mean) could be noticed for majority of the traits, the highest being for protein content and fruit yield. Correlation analysis indicated that most of the character combinations had higher genotypic correlation coefficients than phenotypic, though both had the same direction. Fruit yield displayed positive genotypic association with leaf area, fruits planr', average fruit weight, fruit length, fruit girth, seeds fruir', plant duration and protein content and negative correlation with days to first flower, pollen sterility and incidence of fruit and shoot borer and YVM (except at 50 DAS). Among the thirteen component traits which had high association with fruit yield the maximum positive and negative direct effects were exerted by plant duration and days to first flower respectively. Maximum indirect effects were exerted by fruits planr' in positive direction and by leaf axil bearing first flower in negative direction and both these were through days to first flower. Selection indices were computed utilising yield and its thirteen components and eight genotypes were chosen. Among these, five high yielding but YVM susceptible types,'iz., NBPGRI TCR-2020 (L.), NBPGR/TCR-1498 (L2), NBPGR/TCR (LJ), MDU-) (L..) and NBPGR/TCR-985 (Ls) were used as lines and NBPGR/TCR-2060 (T d, Parbhani Kranti (T2) and Varsha Uphar (TJ) were used as testers for crossing programme. '=-

5 During line x tester progl'amme, high values of ~ca and sea etlects were noticed for fruit yield and leaf area. L5 was the most superior line which excelled with respect to mean performance and general combining ability for yield average weight and length of fruits and leaf axil bearing first flower along with low YVM incidence. Among the testers T2was the best being superior fruits. for yield, number, average weight, girth and ridges of Out of the fifteen hybrids, overall performance with respect to per se performance, standard heterosis and sea effects was superior for L2 x T I (NBPGR/TCR-1498 x NBPGR/TCR-2060) with respect to days to first flower, leaf area, pollen sterility, fruits planrl, average fruit weight, fruit weight planrl, fruit length, fruit girth, seeds fruir' and YVM resistance. Other excellent hybrids were L5 x T2 (NBPGR/TCR-985 x Parbhani Kranti).J L:I x T 2 (NBPGR/TCR x Parbhani Kranti) and L~ x T, (MDU-I x Varsha Uphar) These four selected crosses were utilised for generation mean analysis in order to detect the gene action with regard to 22 traits including incidence of leaf roller and leaf spot. Presence of epistasis was tested and subsequently interaction effects vi::., additive x additive, additive x dominance and dominance x dominance effects were computed. Duplicate epistasis was more prevalent than complementary in majority of the cases. Predominance of additive and additive x dominance interaction in cross L2 x T I for yield and average fruit weight suggests its suitability for direct selection and recombination breeding. Cross L5x T2 could be utilised for heterosis breeding and selection, directly or in segregating generations, in order to improve yield, average fruit weight and YVM resistance owing to the prevalence of dominance and additive x additive components. The gene effects were absent, non-significant or undesirable in cross L:I x T 2.YVM resistance in L4 x T:I could be improved through heterosis breeding, direct selection and recombination breeding due to the presence of negatively significant dominante and additive x additive components.