The reproductive biology of okra. 2. Self-fertilization kinetics in the cultivated okra (Abelmoschus esculentus), and consequences for breeding

Summary The use of Cruden's index (1977), for studying okra sexual reproductive allocations, indicates a facultative autogamy mode. The purpose of the research described is to obtain more accurate information on the self-fertilization process. For this, self-pollen grain germination was stopped at different times of the day. Twelve varieties of Abelmoschus esculentus were used. Self-fertilization kinetics—expressed by the setting rate—displayed an increase between 7.00 to 16.00 hr. Study of obtained progenies, by stimulated allogamy, confirmed the process and showed that allo-pollen grains deposited on a stigma after midday had only a very little chance of contributing to fertilization. As a result, the polymorphism of the flower structure and particularly the distance between anther and stigmas, insect types and movement habits play major roles in governing okra allogamy. We also show that self-fertilization kinetics can be used to improve controlled hybrid production.     

Future prospects of the genetic integrity of two species of okra (Abelmoschus esculentus and A. caillei) cultivated in West Africa

Summary A study of the geographical distribution of two species of okra, Abelmoschus esculentus and A. caillei, shows that both are cultivated in almost all villages from the Gulf of Guinea to the southern limit of the Sahel. If the cultivars of both species, collected in the same village, are sown simultaneously, as often is the case, study of flowering reveals the possibility of interspecific pollination during about 7 weeks to 2 months. Interspecific hybrids can be obtained artificially, but at experimental stations and in the field very low rates of cross fertilization are observed. In addition, the sterility of the F1 hybrids makes their genetic participation in subsequent generations unlikely. In this study, we show that: 1) although grown for the same purpose, the two species are clearly managed as two separate crops by local growers; 2) the conditions which allow gene flow between both crops exist, and 3) the rate of spontaneous introgressions is low. The genetic integrity of the two species does not, therefore, seem threatened and the relative balance between them is mainly tied to the choice of the growers.     

Effectiveness and relative discriminatory abilities of techniques measuring genotype × environment interaction and stability in okra (Abelmoschus esculentus (L) Moench)

Summary Twenty selected okra genotypes were evaluated in four different environments for stability of performance, measured by days to flowering, number of branches per plant, plant height, number of pods per plant, pod weight, and pod yield per plant. An analysis of the components of G × E interaction showed that it might not always be adequately explained by a linear function of the environment. The heritability estimates for the response of the characters showed that the number of branches per plant was under strong genotypic influence. The stability variance parameters, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaaiaacaqabeaadaqaaqaaaOqaaiqbeo8aZzaaja% WaaWbaaSqabeaacaaIYaaaaaaa!3A18!\[\hat \sigma ^2\]and W-mean square and the deviation MS employed in the analyses of stability indicated that most of the genotypes were unstable in respect of the characters. The % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaaiaacaqabeaadaqaaqaaaOqaaiqbeo8aZzaaja% WaaWbaaSqabeaacaaIYaaaaaaa!3A18!\[\hat \sigma ^2\]and W-mean square produced similar results which were different from those of deviation MS; the two stability-variance techniques were more discriminatory than the regression technique.     

Effects of the okra leaf,nectariless, frego bract and glabrous conditions on yield and quality of cotton lines

Summary Effects on yield and quality associated with the glabrous leaf, frego bract, okra leaf and nectariless genes (singly and combined) were studied under two insecticide spray regimes (heavy and light) in field experiments repeated over three seasons. Under the heavy spray regime there were few consistent differences between mutant genotypes and the normal except for low yields associated with the glabrous leaf, nectariless, frego bract genotype and the okra leaf genotype. Under the light spray regime, genotypes containing the okra leaf gene and/or the nectariless genes were associated with higher yields than the normal and genotypes containing glabrous leaf and/or frego bract genes were associated with lower yields. Positive epistatic interactions occurred in a number of instances including the okra leaf gene in the glabrous hair, normal bract background under heavy spraying, and with all backgrounds under light spraying, and for glabrous leaf in both the okra normal and okra frego backgrounds under heavy spraying. Nectariless also interacted positively with the normal leaf, normal hair, normal bract background under light spraying. Pronounced negative epistatic interactions only occurred in the light spray regime, and included glabrous leaf in all backgrounds, and frego bract in all backgrounds except the normal leaf, normal hair. The mutant genes had only minor effects on lint quality. The implications of the results for breeding and pest management are diseussed.     

Genetics of resistance to early blight (Alternaria solani Sorauer) in tomato (Lycopersicon esculentum L.)

The genetic nature of early blight resistance in tomato was studied in three crosses at seedling and adult plant stages. A six generation mean analysis of the cross Arka Saurabh (susceptible) × IHR1939 (resistance) and its reciprocal cross revealed that the resistance to early blight was conferred by recessive polygenes at both seedling and adult plant stages. This polygenic early blight resistance revealed the importance of additive and additive × additive gene effects at seedling stage and higher magnitude of dominance and dominance× dominance gene effects at adult plant stage. Evaluation of parents, F₁, F₂ and backcross generations of IHR1816 (resistance) × IHR1939 (resistance) revealed that the early blight resistance genes in IHR1816 (Lycopersicon esculentum NCEBR-1) and IHR1939 (Lycopersicon pimpinellifolium L4394) are independent. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetics of two mechanisms of resistance to Meloidogyne naasi (FRANKLIN) in an Aegilops variabilis Eig. accession

Summary Accession No. 1 of Aegilops variabilis has complete resistance to the root knot nematode, Meloidogyne naasi. F2 segregation in a cross between this and two susceptible accessions showed that one dominant gene named Rkn-mn1 prevented development of galls on the roots and consequently of female nematodes. The study of the numbers of females in galls on the F2 plants allowed detection of a recessive gene, Rkn-mnAv, suppressing development of J2 larvae into females. The presence of Rkn-mnAv also resulted in a decrease of the level of galling. Rkn-mn1 has already been introduced into wheat. The interest in transferring also Rkn-mnAv is discussed in relation to extending durability of the nematode resistance.     

Genetics of resistance to Aphis craccivora in cowpea

Summary Inheritance of aphid resistance and allelic relationships among sources of resistance was studied in the parents, F₁, F₂, F₃, and backcross populations of cowpea crosses. Each 4-day old seedling was infested with five fourthinstar aphids. Seedling reaction was recorded 14–16 days after infestation when the susceptible check was killed. The segregation data from eight crosses between resistant and susceptible cowpea cultivars indicated that aphid resistance was inherited as a monogenic dominant trait. Segregation data from crosses among eight resistant cultivars indicated that one or two loci and modifier(s) were involved in the expression of resistance to aphids. It was suggested that further studies on allelism among sources of resistance needed to be conducted in order to resolve this.     

Sources of resistance to tomato-yellow-leaf-curl-virus (TYLCV) in Lycopersicon species

Summary Sources of resistance to tomato-yellow-leaf-curl-virus (TYLCV) were investigated in 16 accessions of three Lycopersicon species and 55 commercial tomato hybrids and cultivars. All commercial hybrids and cultivars were highly susceptible. Accessions of L. hirsutum, L. hirsutum f. glabaratum and L. pimpinellifolium showed a wide range of reactions. Those of L. peruvianum, LA 385 of L. peruvianum f. humifusum exhibited very high levels of resistance indicating their potential use in local breeding programs. In contrast to earlier findings, back indexing showed that all symptomless genotypes in this investigation were carriers of the TYLCV.     

Variation in Okra

Summary A study of the variation of 29 characteristics of 585 varieties or seedlings of okra revealed that 17 West African varieties could be distinguished from all others on the basis of 5 discriminating characteristics. In addition, seedlings of the 3rd outcrossing generation of a population differed from a varietal collection in several characteristics, the most important of which were more seeds per pod and more pods per plant. This is believed to be the result of mass-selection. Country groups differed significantly in characteristics but these differences are believed to be due to small sample size. No such distinguishing characteristics were evident among country groups represented by large numbers of varieties.     

Genetics of resistance to ascochyta blight in chickpea (Cicer arietinum L.)

Summary Six chickpea lines resistant to Ascochyta rabiei (Pass.) Lab. were crossed to four susceptible cultivars. The hybrids were resistant in all the crosses except the crosses where resistant line BRG 8 was involved. Segregation pattern for diseases reaction in F₂, BCP₁, BCP₂ and F₃ generations in field and glasshouse conditions revealed that resistance to Ascochyta blight is under the control of a single dominant gene in EC 26446, PG 82-1, P 919, P 1252-1 and NEC 2451 while a recessive gene is responsible in BRG 8. Allelic tests indicated the presence of three independently segregating genes for resistance; one dominant gene in P 1215-1 and one in EC 26446 and PG 82-1, and a recessive one in BRG 8.Research paper No. 3600     

Effects of recurrent selection for resistance to scab (Gibberella zeae) in wheat

Summary Scab caused by Gibberella zeae Petch., in common wheat, is one of the most severe diseases in China. A source population C0, bred for scab resistance, was developed through three cycles of multiple-parent crossing and intercrossing by means of the dominant male-sterile gene Ta1 (Ms2), according to Wu's scheme. Phenotypic recurrent selection methods for increasing the resistance to scab-infection of spikelets and seeds with the male-sterile plants were carried out simultaneously in Nanjing and Shanghai and at Jianyang, Fujian Province, for three cycles. The generations from C0 to C3 and two check cultivars were evaluated, using a randomized block design, under conditions of an artificially induced epidemic of scab during 1988–1990. The results indicate that there were significant differences in the resistance to scab between these generations. On average, the percentages of diseased spikelets and seeds of the male-fertile plants were reduced by 9% and 10%, respectively. The frequency of resistant plants was distinctly enhanced by recurrent selection. Analysis of variance showed that no significant differences existed between cycles of recurrent selection in agronomic characters such as plant height, spikes per plant, spike length, numbers of spikelets and seeds per spike, weight of seeds per spike and 100-kernel weight, days to heading and to maturity. Except for plant height, most of these traits tended to be slightly improved with improvement of resistance in the gene pool. The variance for resistance in the generations was decreased under selection. Recurrent selection for scab resistance using the dominant male-sterile gene Ta1 (Ms2) was both an effective and feasible breeding method for producing this character in wheat.     

Genetics of resistance to five strains of turnip mosaic virus in Chinese cabbage

Summary Inheritance of resistance to turnip mosaic virus (TuMV) strains C1, C2, C3, C4, and C5 in Chinese cabbage (Brassica campestris subsp. pekinensis) was evaluated using monoclonal antibodies. Crosses were made between a resistant line, 0–2, and four susceptible line. Seoul (SE),SSD31 (SS), Cheongbang (CH), and Yaki 1 ho (YA), to determine the inheritance of resistance of 0–2 in different genetic backgrounds. Resistance to TuMV was controlled by a single dominant gene or double dominant genes depending on the strain and cross. The resistance genes of 0–2 were modified by susceptible parents such that a single dominant gene was involved in the SS×0–2 combination, but double dominant genes in the SE×0–2 against TuMV-C3 or TuMV-C5. ELISA tests using inoculated and noninoculated leaves in the same plant suggested that the dominant resistance genes inhibit virus movement rather than virus multiplication.     

Genetics of resistance to Puccinia graminis tritici and Puccinia recondita tritici in Kenya Plume wheat

Summary Seven genes, viz. Sr5, Sr6, Sr7a, Sr8a, Sr9b, Sr12 and Sr17 were associated with seedling resistance to Puccinia graminis tritici in Kenya Plume wheat. The predominant field cultures were avirulent on seedlings with Sr7a, but possessed virulence for the other six genes. However, Sr7a did not confer adult-plant resistance when present on its own. Adult-plant resistance was attributed to Sr2 and possibly also to the interaction of Sr7a and Sr12.Two genes, Lr13 and Lr14a, were identified in seedling tests with various cultures of Puccinia recondita tritici. Lr13 conferred adult-plant resistance to the predominant field strains. Genetic recombination between Lr13 and Sr9b was estimated at 17.6±3.1%.     

Breeding for resistance to neck rot (Botrytis allii) in onions (Allium cepa)

Summary For 10 years the method developed by Van der Meer et al, (1970) to test neck rot resistance in onions has been applied in a breeding programme. From experiments with market varieties, inbred lines and half-sib families it is concluded that neck rot resistance as determined by this method is a quantitative character, which shows continuous variation and is in part fixable by selection. The practical importance of this type of neck rot resistance is not yet clear.Report no. 68     

Genetics of disease resistance in urdbean (Vigna mungo (L.) Hepper) to the leaf spots caused by Colletotrichum truncatum (Schw.) Andrus & Moore

Summary The resistance sources among various test cultivars of urdbean to Colletotrichum truncatum, a leaf spotting pathogen, were identified and genetics of resistance was worked out by studying F₁, F₂ and F₃ generations of crosses between resistant cultivars and the susceptible cv. Kulu 4 and of those among the resistant parents. The resistance was found to be controlled by single dominant genes and the resistance genes were non-allelic.     

Genetics and population improvement of resistance to bacterial soft rot in Chinese cabbage

Resistance to bacterial soft rot caused by Erwinia carotovora subsp. carotovora is a quantitative trait. The narrow-sense heritability was from 42% to 60% in the studied populations. Griffing's diallel analysis and generation mean analysis indicated that additive genetic effects were most significant, and the resistant sources involved in this study appeared to have different genes or alleles. Recurrent phenotypic selection was used for improving the resistance level by combining different resistance genes from the selected genotypes of Chinese cabbage. After 3 cycles of recurrent selection, the level of resistance increased markedly. When the cycle 3 population was compared with the cycle 0 population, the mean disease severity rating was reduced 38% from 6.3 to 3.9, and the percentage of plant survival increased from 65% to 97% based on the mean of two years experiments using mist-chamber seedling inoculation methods. The improvement of resistance was also demonstrated in field assays. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance of resistance to late blight (Phytophthora infestans) in potato

Under epiphytotic conditions for late blight in spring seasons, data were recorded on its intensity four times at 4 days intervals from the start of the disease in the field, in 114 (19 females × 6 males) progenies and their parents planted in randomized complete block design in the years 2005 and 2006. Regression and stepwise regression analysis showed that observations during the rapidly increasing phase of disease between initial and last phase of disease are more important than the observations at initial and last phase of the disease. Combining ability analysis on a sub-set of 68 progenies showed that the additive component of genetic variance was more important than the non-additive component of variance in inheritance of quantitative resistance to late blight. The per se performance of the parents does give an idea about their general combining ability (GCA). However, selection of parents based on their GCA will be very useful for breeding for quantitative resistance to late blight. Parents JX 90, JF 4841, CP 3356, CP 1358, CP 3290, JN 1197 and CP 3125 were found to have good GCA for quantitative resistance for late blight and the best six crosses for late bilght resistance based on mean performance involved parents with good combining ability only.     

Genetics of resistance to 3 isolates of Ascochyta fabae on Faba bean (Vicia faba L.) in controlled conditions

Summary Genetics of resistance to Ascochyta fabae Speg. in Vicia faba L. was studied with a final objective to develop resistant faba bean varieties to Ascochyta blight. The study was conducted separately on 3 single spore isolates (AF10-2 and AF13-2 from Tunisia and AF4-3 from France) and belonging to different groups of virulence (GV1 and GV2). Important general combining ability (GCA) effects were found especially with isolates AF10-2 and AF4-3. Specific combining ability (SCA), although significant for the 3 isolates, was important only with AF13 -2, but less important than GCA. Additive gene effects were predominant to non-additive effects. Lines 29H and A8817 transmitted to their progenies resistance to the 3 isolates, whereas 14–12 and 19TB conferred resistance to their progenies only with isolates AF13-2 and AF4-3, respectively. In the material studied, resistance was generally controlled by dominant genes but also could be attributed to recessive genes although less frequent. Analysis of segregation in the F2 of 2 crosses between the resistant lines (A8817 and 29H) and the susceptible line (14–12) with isolate AF4-3 revealed dominant monogenic control at the level of leaves in the 2 resistant lines and, in addition, a recessive gene controlling resistance of stems. Non-allelic interactions were occasionally manifested and their origin appeared to be due to line 19TB. A recurrent selection scheme was proposed with the objective to develop improved open-pollination populations and synthetic varieties responding to the objective of the national Tunisian research programme on faba bean.     

Inheritance of seed resistance to bruchids in cultivated mungbean (Vigna radiata, L. Wilczek)

Bruchid beetles or seed weevils are the most devastating stored pests of grain legumes causing considerable loss to mungbean (Vigna radiata (L.) Wilczek). Breeding for bruchid resistance is a major goal in mungbean improvement. Few sources of resistance in cultivated genepool were identified and characterized, however, there has been no study on the genetic control of the resistance. In this study, we investigated the inheritance of seed resistance to Callosobruchus chinensis (L.) and C. maculatus (F.) in two landrace mungbean accessions, V2709BG and V2802BG. The F₁, F₂ and BC generations were developed from crosses between the resistant and susceptible accessions and evaluated for resistance to the insects. It was found that resistance to bruchids in seeds is controlled by maternal plant genotype. All F₁ plants derived from both direct and reciprocal crosses exhibited resistance to the bruchids. Segregation pattern of reaction to the beetles in the F₂ and backcross populations showed that the resistance is controlled by a major gene, with resistance is dominant at varying degrees of expressivity. Although the presence of modifiers was also observed. The gene is likely the same locus in both V2709BG and V2802BG. The resistant gene is considered very useful in breeding for seed resistance to bruchids in mungbean.     

Genetic analysis of resistance to Karnal bunt (Tilletia indica,Mitra) in bread wheat

Summary Karnal bunt caused by Tilletia indica in wheat seriously affects the quality of the grains. It is important to generate information on the genetics of resistance to this pathogen so as to aid resistance breeding. For this purpose, four Karnal bunt-resistant lines from China, Brazil and CIMMYT (International Maize and Wheat Improvement Center) and a susceptible Indian cultivar, WL711, were used. The parents, F1 and F3 progenies of five parental diallel crosses revealed that independently segregating loci with three partial dominant resistance alleles were involved in the resistance of Karnal bunt. Lines RC7201/2^*BR2 and Roek//Maya/NAC carried one locus for resistance while Shanghai#7 and Aldan/IAS58 have two and three loci, respectively. One common locus was present in all four resistant parents, which imparted a high level of resistance.