Heterosis in relation to genetic divergence in maize (Zea mays L.)

Summary The magnitude of heterosis was examined in relation to genetic divergence among 10 parents in a 10 × 10 diallel cross of maize. The 10 parents (varieties) were selected on the basis of multivariate analysis of quantitative characters using Mahalanobis' D²-statistic from a lot of 64 varieties of maize belonging to different geograshical regions of the world. The magnitude of heterosis for grain yield and its components was found to be higher with moderate (intermediate) parential diversity than with extreme ones. The results indicated that not only the genetic diversity but the high per se performance with respect to specific characters of interest should be taken into consideration also while selecting parents for hybridization.     

Identification and inheritance of male sterility in groundnut (Arachis hypogaea L.)

Summary Some plants without pods but with gynophores were observed in two F₄ progenies of two crosses of goundnut (Arachis hypogaea L.). The flowers on these plants had translucent white anthers with no or a few sterile pollen grains. Three such plants in the succeeding generation were hand pollinated with pollen from a short-duration Indian cv. JL 24. The resulting F₁ hybrid plants (male sterile x JL 24) were normal. Chi-square tests for segregation for male fertile and male sterile plants in F₂ and F₃ generations indicated that the male sterility in these crosses of groundnut is governed by two recessive genes. We designate these genes as ms₁ and ms₂ with ms₁ms₁ms₂ms₂ being a male sterile genotype.Submitted as ICRISAT J. A. No. 1812.     

Inheritance of albinism in certain interspecific and intersubspecific crosses in groundnut (Arachis hypogaea L.)

Summary A study of the several interspecific and inter-subspecific crosses indicated that albinism in groundnut is recessive and in these crosses is controlled by triplicate recessive loci.ICRISAT Paper No. JA-336     

Inheritance of two components of early maturity in groundnut (Arachis hypogaea L.)

Summary Knowledge of inheritance of early maturity or its components is important to groundnut breeders in developing short-duration cultivars. This study was conducted to determine the inheritance of two components of early maturity: days to first flower from sowing, and days to accumulation of 25 flowers from the appearance of first flower, using three groundnut genotypes. Two early-maturing (Chico and Gangapuri) and one late-maturing (M 13) genotypes were crossed in all possible combinations, including reciprocals. The parents, F₁, F₂, F₃, and backcross populations were evaluated for days to first flower from sowing, and for days to accumulation of 25 flowers. The data suggest that days to first flower in the crosses studied is governed by a single gene with additive gene action. Chico and Gangapuri possess the same allele for this component of earliness. Three independent genes with complete dominance at each locus appear to control the days to accumulation of 25 flowers. In crosses between late (M 13) and early (Chico or Gangapuri) parents, a segregation pattern suggesting dominant-recessive epistasis (13 late:3 early) was observed for this component. Segregation in the F₂ generation (1 late:15 early) of both early parents (Chico x Gangapuri) indicated that the genes for early accumulation of flowers in these two parents are at different loci.Submitted as ICRISAT J.A. No. 1557.     

The role of mutations in intraspecific differentiation of groundnut (Arachis hypogaea L.)

Summary Based on morphological diversity, cultivated groundnut (Arachis hypogaea L.) is classified into two subspecies (fastigiata and hypogaea) and further into four botanical types (Spanish bunch, Valencia, Virginia bunch and Virginia runner). In a cross between two Spanish cultivars belonging to ssp. fastigiata, a true breeding variant (Dharwad early runner) sharing some characters of both the subspecies was isolated. The variant, on mutagenesis with ethyl methane sulphonate (EMS) yielded a very high frequency of mutants resembling all four botanical types. Some of the mutants produced germinal reversions to Dharwad early runner in later generations indicating genetic instability. While most of the revertants bred true, some of the mutants continued to segregate, wherein each botanical group of mutants produced all other botanical types. A detailed analysis of the breeding behaviour of mutants revealed several unusual features (such as homozygous mutations, mutation outbursts, segregation distortions, somatic mutations and multiple character mutations) that could not be explained through conventional mutation theory. In the light of these findings, the role of mutations in evolutionary differentiation of the crop and the probable mode of their origin have been discussed.     

Analysis of diallel cross for some physical-quality traits in peanut (Arachis hypogaea L.)

The combining abilities for physical-quality traits in peanut were examined to understand the type of gene action governing these traits, and to identify peanut genotypes suitable for use as parents in breeding for quality improvement. The F₁ hybrids including reciprocals from a six-parent diallel cross along with the parents were evaluated in a randomised complete block design. Data were recorded on five quality traits in peanut viz., shelling outturn, 100-pod weight, 100-seed weight, Count and proportion of sound mature seeds. Substantial genetic variability was observed among the hybrids for the traits studied. Diallel analysis indicated that expression of majority of the quality traits is regulated predominantly by additive gene action suggesting possibility of early-generation selection, while non-additive gene action also plays an equally important role in the control of seed size. Significant reciprocal effect for all the traits denoted role of maternal parent in the expression of quality traits and importance of parental selection in quality breeding. Genotypes ICGV 86564 and TPG 41 were good combiners for seed size, while J 11 was a good combiner for improvement of shelling outturn and proportion of mature seeds. Association between general combining ability (GCA) effects and mean performance suggested that the performance per se of the genotype should be a good indicator of its ability to transmit the desirable quality attributes to its progenies. Though performance of crosses was found to be independent of parental GCA status, it is evident that at least one of the parents used in hybridisation should have large pods and seeds for obtaining better segregants.     

Heterosis and combining ability in hybrids among 12 commercial varieties of sesame (Sesamum indicum L.)

Heterosis and combining-ability effects were studied in the parents and 66 F₁ hybrids from a diallel cross of 12 elite sesame varieties in five different environments in Venezuela. The mean yield of the hybrids was clearly superior to the parental mean in all five locations. There were three heterotic hybrids that showed a higher yield than controls in all environments. The best hybrid in each place yielded significantly better than the best cultivar, the differences ranging from 28 to 109%. Specific combining-ability (SCA) effects were more important than general combining-ability (GCA) in four of the environments. A large genotypexlocation interaction was found for all traits, suggesting that hybrids should be produced for specific locations. ‘Arawaca’ and ‘Piritu’ should be chosen as parents for any sesame-breeding programme in view of their large GCA effects.     

Genetics of nonnodulation in groundnut (Arachis hypogaea L.). Studies with single and mixed Rhizobium strains

Summary Genetic studies of nonnodulation in groundnut were carried out in a cross, NC 17×PI 259747, with a single Rhizobium strain, NC 92, and a native Rhizobium population.The normal nodulation of the parents, F₁ generations and backcross progenies, and the F₂ segregation for nodulation and nonnodulation confirmed that nonnodulation in groundnut is controlled by two duplicate recessive genes.Approved ICRISAT Journal Article No. 211.     

Reciprocal cross differences in a 6×6 diallel set of groundnut (Arachis hypogaea L.) in the F1 generation

Summary Reciprocal cross differences were studied in a 6×6 diallel full set comprising of thirty hybrid combinations of groundnut in the F₁ generation.Reciprocal cross differences were observed for growth habit in four pairs of crosses, for leaf colour, flower colour and stem pigmentation in two pairs of crosses each. It was observed that the inheritance of flower colour, stem pigmentation and testa colour which exhibited different shades of purple colour was likely to be governed by pleiotropic gene(s). Among the quantitative characters significantly positive reciprocal effects were observed in different crosses for number of mature pods per plant, weight of pods per plant and shelling percent. Marked reciprocal cross differences were observed for pod and kernel characters like pod filling, pod beak, pod constriction and testa colour.     

Components of resistance to late leaf spot and rust among interspecific derivatives and their significance in a foliar disease resistance breeding in groundnut (Arachis hypogaea L.)

Late leaf spot (LLS) and rust cause substantial yield losses and reduce the fodder and seed quality in groundnut (Arachis hypogaea L.). Adoption of resistant cultivars by the semi-arid tropic farmers is the best option to overcome yield losses. Knowledge on components of resistance to these diseases should facilitate the development of groundnut cultivars with enhanced resistance to LLS and rust. The objectives of the experiments were to study the genetic variability and relationships among components of resistance to LLS and rust, and assess their significance in disease resistance breeding. Fifteen interspecific derivatives for LLS and 14 for rust and a susceptible control, TMV 2, were evaluated in a randomised complete block design with two or three replications under greenhouse conditions. The experiments were repeated twice. Genotypic differences were highly significant for all the traits studied. Resistance to LLS is due to longer incubation and latent periods, lesser lesions per leaf, smaller lesion diameter, lower sporulation index, and lesser leaf area damage and disease score. Selection based on components of resistance to LLS may not lead to plants with higher retained green leaf area. The remaining green leaf area on the plant should, therefore, be the major selection criteria for resistance to LLS in breeding programs. Resistance to rust is due to longer incubation and latent periods, fewer pustules per leaf, smaller pustule diameter, lower sporulation index, and lesser leaf area damage and disease score. Rust resistant components appear to work additively, therefore, selection based on resistance components together with green leaf area retained on the plant should be the basis of selecting for resistance to rust in breeding programs. ICGV 99005, 99003, 99012, and 99015 for rust and ICGV 99006, 99013, 99004, 99003, and 99001 for LLS are the better parents for use in resistance breeding programs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on genetic divergence in potato

Summary Sixty-seven potato varieties/hybrids were grouped in 15 clusters on the basis of D² values. The clustering pattern was not influenced by the geographic diversity of the varieties. However, a segregation between varieties of the Tuberosum and Andigena type varieties was observed. The exotic potato varieties and also the Indian varieties bred from Tuberosums showed a poor divergence. In contrast, the divergence in the varieties developed from Tuberosum-Andigena crosses was much greater. The inter-cluster distance of such varieties, with respect to Tuberosum and Andigena clusters, appeared to be influenced by the cytoplasm they carried. The varieties with Tuberosum cytoplasm were closer to clusters having Tuberosum varieties and those with Andigena cytoplasm were closer to clusters having Andigena type varieties. The characters least influenced by the selection during the course of evolution of the present day varieties were found to be mainly responsible for adding divergence to the population. A breeding plan involving varieties from different clusters has been outlined.     

Ribosomal DNA repeat unit polymorphism and heritability in peanut (Arachis hypogaea L.) accessions and related wild species

Repeat unit length and restriction site variation in ribosomal RNA geneclusters (rDNA) was surveyed in 77 Arachis accessions, includingsamples from 39 accessions of cultivated Arachis hypogaea(2n=4x=40), 36 accessions representing 15 related tetraploid and diploidwild species, and two synthetic amphidiploids. Total genomic DNA wasdigested with five restriction enzymes, and probed with three heterologousribosomal clones of wheat and broad bean. Four rDNA repeat unit lengthclasses were recognized in the Arachis species. Restriction site analysisshowed that some SacI, BamHI and TaqI cleavage sites in rDNA unit werehighly conserved. With few exceptions, the variable BamHI and EcoRV siteswere able to differentiate the taxonomic sections and species, respectively.Arachis hypogaea and A. duranensis accessions produced fourrDNA length classes. Among these, three were identical with those of otherArachis species. A SacI restriction site (s) from probe (Ver6-5) cangenerally distinguish the two subspecies A. hypogaea ssp. hypogaea and A. hypogaea ssp. fastigiata. Forty nine per centof bands were polymorphic across the A. hypogaea accessionsanalysed. This study does not support A. batizocoi to be a progenitorof A. hypogaea. For the gene array, the contribution from eachparental genome can be detected in the two synthetic amphidiploids.     

Effects of cytoplasm on heterosis and combining ability for agronomic traits in rice (Oryza sativa L.)

Summary Effect of sterilizing (WA) cytoplasm on heterosis and combining ability for days to flowering, plant height and grain yield in rice was studied in 70 crosses and their reciprocals produced by 10 cytoplasmic male sterile (A), their maintainer (B) and seven restorer (R) lines following line x tester design. The materials consisting of 140 hybrids (70 A/R and their reciprocal 70 R/B) plus 17 parental lines (10 B + 7 R) were evaluated under six environments, created by growing in three fields with different fertilizer doses (0, 60, 120 kg N/ha) and 2 seasons (dry and wet) during 1986 at IRRI farm. Reciprocal cross effect (A/R vs R/B) were highly significant for all the three traits. Interaction of reciprocal cross effects with environments were also highly significant for yield and days to flowering. Cytoplasmic effect for yield, days to flowering and plant height were estimated by comparing A/R and R/B combination and testing the significance of difference with LSD value. In order to avoid confounding effect of spikelet sterility on yields, twenty crosses showing normal spikelet fertility were selected. Both positive and negative cytoplasmic effects were observed for the three traits. The effects were modified by environments, except for plant height. Heterosis for all three traits was also affected by cytoplasm, however, manifestation of cytoplasmic effects was higher for heterosis for days to flower than in heterosis for yield and plant height. Effect of cytoplasm was more pronounced on general combining ability effects of parents than specific combining ability effects of crosses. Among the parents two CMS lines A4 (IR54752A) and A8 (IR22107-113-3-3A) and two R lines: R2 (IR46) and R7 (IR9761-19-1) showed consistent positive effect of cytoplasm on general combining ability. These lines have given several good heterotic combinations. The study indicated the usefulness of evaluating diverse cytoplasmic sources in various nuclear genotypes bred for hybrid rice breeding program.     

转Bt抗虫棉与常规棉品种间配合力分析及杂种优势研究

 利用6个抗虫棉品种作母本,4个常规品种作父本,按NCⅡ设计,对24个组合的杂种F₁进行了分析。结果表明,杂种F₁具有明显的优势,所研究的13个性状全部具有中亲优势,9个性状具有高亲优势,11个性状具有竞争优势。配合力分析的10个性状中单株铃数、铃重、纤维长度、纤维伸长率和麦克隆值主要受基因的加性效应控制,而子棉产量和皮棉产量主要受基因的非加性效应影响。鲁棉研17是优良的抗虫棉亲本,而冀棉12 是良好的非抗虫棉亲本,组合鲁棉研17×中棉所12在重要农艺性状上优势明显,相对而言纤维品质的改良较难。     

RAPD markers linked to a rust resistance gene in cultivated groundnut (Arachis hypogaea L.)

Groundnut rust (Puccinia arachidis Speg.) is an important air borne pathogen, which causes substantial losses in groundnut yield and quality. Although large numbers of accessions were identified as rust resistant in wild, interspecific derivative and cultivated groundnut species, transfer of resistance to well-adapted cultivars is limited due to linkage drag, which worsens yield potential and market acceptance. A F₂ mapping population comprising 117 individuals was developed from a cross between the rust resistant parent VG 9514 and rust susceptible parent TAG 24. Rust resistance was governed by single dominant gene in this cross. We identified 11 (out of 160) RAPD primers that exhibited polymorphism between these two parents. Using a modified bulk segregant analysis, primer J7 (5′CCTCTCGACA3′) produced a single coupling phase marker (J7₁₃₅₀) and a repulsion phase marker (J7₁₃₀₀) linked to rust resistance. Screening of the entire F₂ population using primer J7 revealed that the coupling phase marker J7₁₃₅₀ was linked with the rust resistance gene at a distance of 18.5 cM. On the other hand, the repulsion phase marker J7₁₃₀₀ was completely linked with rust resistance. Additionally, both J7₁₃₀₀ (P = 0.00075) and J7₁₃₅₀ (P < 0.00001) were significantly associated with the rust resistance. Marker J7₁₃₀₀ identified all homozygous rust resistant genotypes in the F₂ population and was present in all the eight susceptible genotypes tested for validation. Thus, J7₁₃₀₀ should be applicable for marker-assisted selection (MAS) in the groundnut rust resistance breeding programme in India. To the best of our knowledge this is the first report on the identification of RAPD markers linked to rust resistance in groundnut.     

The probable genome donors to Arachis hypogaea L. based on arachin seed storage protein

Summary Interrelationships among six diploid species (A. chacoense, A. villosulicarpa, A. batizocoi, A. correntina, A. duranensis and A. cardenasii), tetraploid wild groundnut A. monticola and four accessions of A. hypogaea were studied by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) of total seed proteins and arachin immunoprecipitates. Arachin in A. monticola and A. hypogaea cv. Trombay Groundnut 9 (TG-9) was composed of four acidic subunits (47.5 kd, 45.1 kd, 42.6 kd and 41.2 kd) and one major basic subunit (21.4 kd). The arachin subunit pattern in cv. Spanish Improved (SP) and TG-1 was almost similar to the pattern observed in A. monticola with the exception that the SP lacked the 41.2 kd and TG-1 lacked the 42.6 kd acidic subunits of A. monticola. Seed extracts of all diploid species studied reacted with the anti-arachin antibodies raised against SP arachin. The electrophoretic analysis of immunoprecipitates of diploid species showed a range of acidic subunits from 46.2 kd to 41.2 kd and one or two basic subunits of 21.4 kd and 20.2 kd. None of the diploid species showed the 47.5 kd subunit found in A. monticola or A. hypogaea. Of the diploid species, A. duranensis and A. cardenasii demonstrated two acidic subunits of 45.1 kd and 41.2 kd and a basic subunit of 21.4 kd as found in A. monticola. Likewise A. batizocoi showed two acidic subunits of 45.1 kd and 42.6 kd and the basic subunit of 21.4 kd as was observed in A. monticola. Based on electrophoretic data, our research supports the earlier conclusion that the probable genome donors to A. monticola are A. batizocoi and A. duranensis or A. cardenasii.     

陆地棉显性无腺体品系杂种优势及配合力研究

以７个显性无腺体陆地棉品系和４个常规品种（系）为材料，按ＮＣＩ设计，对２８个组合的杂种Ｆ１进行了分析。结果表明。杂种Ｆ１具有明显的优势，２８个组合所研究的１５个性状中全部具有中亲优势，６个性状具有高亲优势，４个性状具有竞争优势；配合力分析的１１个性状中，株高、衣分、纤维长度和麦克隆值主要受基因加性效应控制，而子棉产量、皮棉产量、单株铃数、铃重和子指等性状同时受基因加性和非加性效应作用，显无０７３是丰产的显性无腺体品系，而显无２６０是较好的优良品系，组合显无０７３Ｘ泗棉２号在重要性上表现较好。     

Heterosis in crisphead lettuce (Lactuca sativa L.) hybrids

Summary Six of 16 F₁ hybrids from diverse crosses of crisphead lettuce with butterhead, cos or other crispheads significantly outyielded their respective better parent. Four were crosses between crisphead and cos parents, one was a butterhead × crisphead cross and one, a winter crisphead × winter crisphead cross. This latter hybrid plus one other also proved heterotic in a subsequent trial of ten crosses involving five winter crisphead parents, with yield excesses over better parent of 16 and 19%. It appeared significant that the heterotic crosses were given by parents of dissimilar origin. Trials of F₂ segregants from one of these heterotic hybrids enabled predictions to be made for 10.2 to 24.1% yield increases over better parent by the retention and clonal multiplication of the 10% highest yielding selections. Heterosis demonstrated in these trials may constitute the first reported cases in lettuce.     

Early generation testing for yield and physiological components in groundnut (Arachis hypogaea L.)

Selection of superior crosses of groundnut (Arachis hypogaea L.) in early generations would increase the probability of identifying superior lines. The objective of this study was to determine the potential of selecting for physiological traits identified in a yield model [crop growth rate (C), reproductive duration (DR) and partitioning (p)] in segregating populations. Forty populations and nine parental lines were evaluated in replicated trials in 1992 (F2, 1993 (F3) and 1994 (F4) at three locations in Niger. Physiological traits were estimated from final yield and biomass as well as data on flowering and maturity. Regressions from two different parent-offspring generations (F2: F3 and F3: F4) were calculated. The results were compared to determine if early generation performance accurately predicts the performance of cross bulks in later generations. Differences were observed among populations and parents for all traits. Effects of locations were significant for C, p and DR in F2 and F3 but nonsignificant for yield and C in F4. Regression coefficients from F3: F2 were 0.10 ± 0.08 for C, 0.45 ± 0.17 for p, 0.10 ± 0.03 for DR and 0.16 ± 0.03 for pod yield. Based on F3: F4 regression, the coefficients were 0.12 ± 0.23 for C, 0.46 ± 0.17 for p and 0.57 ± 0.17 for yield. Parent-offspring correlations were in most cases similar to the regression values. It was concluded that selection for yield and model components in early generation bulks may inneffective. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cytology and leafspot resistance in Arachis hypogaea x wild species hybrids

Summary Introgression of germplasm from diploid wild Arachis species to A. hypogaea has great potential for improving pest resistance in cultivated peanuts. This investigation evaluated methods for incorporating exotic germplasm into cultivated peanuts, especially for Cercospora arachidicola Hori resistance. Interspecific hybrids between A. hypogaea (cvs. NC 2 and NC 5) and the wild species A. cardenasii Krap. et Greg. nom. nud. and A. chacoense Krap. et Greg. nom. nud. were analyzed cytologically and for leafspot resistance. All F₁ hybrids were sterile, had irregular meiosis, and very few multivalents. They were highly resistant to C. arachidicola in field tests and had a 10-fold reduction of conidia per lesion in the greenhouse as compared to A. hypogaea cultivars. After colchicine treatments of F₁ hybrids, hexaploids (2n=60) and aneuploids (2n=54, 56, 63) were observed. The hexaploids had up to 18 univalents per pollen mother cell and very few multivalents, indicating a low frequency of intergenomic chromosome pairing. For C. arachidicola resistance, significant differences were not found among wild species parents, F₁ hybrids and two generations of hexaploids. Most hexaploids were stable at 2n=60 and embryos aborted when backcrosses with the respective wild species were attempted. However, when hexaploids were backcrossed to A. hypogaea, several fertile pentaploid (2n=50) offspring were obtained. Use of self-pollinating pentaploids is believed to be the quickest method to recover 40-chromosome hybrid derivatives in these hybrids.