Segregation distortion of Brassica carinata derived black rot resistance in Brassica oleracea

Three segregating F₂ populations were developed by self-pollinating 3 black rot resistant F₁ plants, derived from across between black rot resistant parent line 11B-1-12 and the susceptible cauliflower cultivar ‘Snow Ball’. Plants were wound inoculated using 4 isolates ofXanthomonas campestris pv. campestris (Xcc) race 4, and disease severity ratings of F₂ plants from the three populations were scored. A total of 860 arbitrary oligonucleotide primers were used to amplify DNA from black rot resistant and susceptible F₂ plants and bulks. Eight RAPD markers amplified fragments associated with completely disease free plants following black rot inoculation,which segregated in frequencies far lower than expected. Segregation of markers with black rot resistance indicates that a single, dominant major gene controls black rot resistance in these plants. Stability of this black rot resistance gene in populations derived from 11B-1-12 may complicate introgression into B. oleracea genotypes for hybrid production. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance of resistance to black rot (Xanthomonas campestris pv. Campestris) in cauliflower (Brassica oleracea var. Botrytis)

Summary Black rot disease caused by Xanthomonas campestris pv. campestris is a limiting factor in the commercial production of the cauliflower crop. Crosses were attempted between SN 445, a mid season cultivar resistant to black rot and two highly susceptible commercial cultivars (Pusa Snowball-1 and K-1). Studies of the F₁'s, F₂'s and back crosses indicated that SN 445, carries a dominant gene imparting resistance to black rot.     

Inheritance of resistance to Pyrenochaeta lycopersici in tomato

Summary Tomato accessions (Lycopersicon sp.), along with commercial cultivars and breeding lines were grown in a field infested with the brown root rot (BRR) organism, Pyrenochaeta lycopersici and evaluated for resistance. Three L. esculentum Mill. accessions, P.I. 260397, P.I. 262906 and P.I. 203231, were resistant and were used as male parents in crosses designed to transfer resistance to tomatoes of fresh market type. Through analysis of parental generations and F₁ and F₂ progenies from three crosses the heritability of resistance in the broad sense was estimated to range from 25 to 43 percent. The minimum number of genes influencing resistance was estimated to be from 4 to 8.Florida Agricultural Experiment Stations Journal Series Paper no. 317.     

Introgression of low temperature tolerance and red rot resistance from Erianthus in sugarcane

Eighteen clones involving Erianthus, as one of the parents, were evaluated in a randomised block design under sub-tropical conditions of Karnal (Haryana, India). Fifteen characters, which contribute towards stalk yield and juice-quality, were studied. The growth of these clones was monitored during peak winter months of December and January. Significant variability existed among the clones for all the traits studied, except for pol % in juice at 10-month crop age, indicating potentiality of the clones to select desirable types. Nine clones showed significant increase in stalk length during winter months over the better standard Co 1148. Whereas 6 clones developed more number of leaves than Co 1148. Both these characters showed high genetic variability, high heritability and hence, high expected genetic gain. Path analysis revealed that these traits contributed about 16%, 5% and 4% to the total genetic variability in juice quality traits (pol % and CCS %), stalk yield and CCS yield, respectively. Growth in winter months has resulted in an increase in stalk yield and CCS yield. This may help in reducing the yield gap between tropical and sub-tropical regions. Majority of clones showed resistance to red rot disease (major disease of sugarcane in sub-tropical region). Hence, hybridization of Erianthus with sugarcane has resulted in introgression of genes for cold tolerance and red rot resistance. As Erianthus is known for its hardiness, resistance, of these clones, to other abiotic and biotic stresses is to be ascertained. This revised version was published online in August 2006 with corrections to the Cover Date.     

Stay green trait: variation, inheritance and its association with spot blotch resistance in spring wheat (Triticum aestivum L.)

One thousand four hundred and seven spring wheat germplasm lines belonging to Indian and CIMMYT wheat programs were evaluated for stay green (SG) trait and resistance to spot blotch caused by Bipolaris sorokiniana during three consecutive crop seasons, 1999–2000, 2000–2001 and 2001–2002. Disease severity was recorded at six different growth stages beginning from tillering to late milk stage. SG trait was measured by following two approaches: difference for 0–9 scoring of green coloration (chlorophyll) of flag leaf and spike at the late dough stage (GS 87) and a new approach of leaf area under greenness (LAUG). Germplasm lines showed a wide range (7–89) for LAUG and were grouped into four viz., SG, moderately stay green, moderately non-stay green and non-stay green (NSG). However, very few (2.2%) lines showed high expression of SG trait, i.e., LAUG >60. LAUG appeared to be a better measure of SG trait than a 0–9 scale. Mean spot blotch ratings of SG genotypes were significantly lower than those of NSG genotypes at all growth stages. Two spot blotch resistant genotypes (Chirya 3 and Chirya 7) having strong expressions of SG trait were crossed with NSG, spot blotch susceptible cv. Sonalika. Individually threshed F₂ plants were used to advance the generations. SG trait and spot blotch severity were recorded in the parents and F₁, F₃, F₄, F₅, F₆ and F_6–7 generations under disease-protected and inoculated conditions. SG trait in the F₁ generation was intermediate and showed absence of dominance. Evaluation of progenies (202–207) in the segregating generations revealed that SG trait was under the control of around four additive genes. Lines homozygous for SG trait in F₄, F₅, F₆ and F_6–7 generations showed significantly lower mean area under disease progress curve (AUDPC) for spot blotch than those with NSG expression. A positive correlation (0.73) between SG trait and AUDPC further indicated a positive influence of SG on severity of spot blotch. The study established that variation for SG trait exists in spring wheat; around four additive genes control its inheritance in the crosses studied and there is positive association between SG trait and resistance to spot blotch.     

Combining ability analysis of resistance to Helminthosporium leaf blight in spring wheat

Wheat breeders in South Asia are attempting to develop wheat (Triticum aestivum L.) cultivars resistant to Helminthosporium leaf blight (HLB), which occurs mainly as a complex of spot blotch caused by Cochliobolus sativus (Ito & Kuribayashi) Drechs. ex Dastur, and tan spot caused by Pyrenophora tritici-repentis (Died.) Drechs. Information on the combining ability for HLB resistance in wheat cultivars of South Asia is not available. This study was undertaken to examine the resistance to HLB in nine genetically diverse wheat parents, and to evaluate their general combining ability (GCA) and specific combining ability (SCA) effects toward determining the genetic basis of disease resistance. Nine parents were crossed in a half-diallel mating design to produce 36 populations. The F₁ and F₂ progenies, and the parents were evaluated in replicated field tests at Rampur, Nepal. Multiple disease scores were recorded, and area under the disease progress curve (AUDPC) was calculated to measure disease severity over time. The combining ability analysis was performed using Griffing's Method 2, Model 1. The parents chosen showed wide variation for resistance to HLB. They and the F₁ and F₂ progenies differed significantly for AUDPC. GCA and SCA effects were significant in both generations suggesting that additive as well as non-additive genetic mechanisms were involved in the expression of resistance in these parents. Wheat genotypes 'SW89-5422', 'G 162', 'NL 781'and 'Chirya 7' had significantly negative GCA effects for AUDPC in both F₁ and F₂ generations, suggesting their prime suitability for use in wheat breeding programs to improve resistance to HLB. The estimate of narrow-sense heritability was 0.77 in both generations suggesting that selection for HLB resistance should be effective in these crosses. The results indicate a predominance of additive gene action in the inheritance of HLB resistance in spring wheat.     

Inheritance of resistance to fruit rot (Phytophthora parasiticaDast.) in tomato (Lycopersicon esculentum Mill.)

Summary Fruit rot disease caused by Phytophthora parasiticaDast. is a limiting factor in tomato production in Himachal Pradesh. 30 to 60 per cent fruits are damaged by this disease. Crosses were made between EC 54725 (Lycopersicon pimpinellifolium), a small tyuited type, resistant to fruit rot and four highly susceptible tomato commercial cultivars (Gola, Sioux, S12, and Lalmani). Studies of F₁'s, F₂'s and back crosses indicated that EC 54725 carries a dominant gene imparting resistance to fruit rot.     

Inheritance of trichomes and resistance to pod borer (Helicoverpa armigera) and their association in interspecific crosses between cultivated pigeonpea (Cajanus cajan) and its wild relative C. scarabaeoides

The legume pod borer, Helicoverpa armigera, is one of the most devastating pests of pigeonpea. High levels of resistance to pod borer have been reported in the wild relative of pigeonpea, Cajanus scarabaeoides. Trichomes (their type, orientation, density and length) and their exudates on pod wall surface play an important role in the ovipositional behavior and host selection process of insect herbivores. They have been widely exploited as an insect defense mechanism in number of crops. In the present investigation, inheritance of resistance to pod borer and different types of trichomes (A, B, C and D) on the pod wall surface in the parents (C. cajan and C. scarabaeoides) and their F₁, F₂, BC₁ (C. cajan × F₁), and F₃ generations has been studied. Trichomes of the wild parents (high density of the non-glandular trichomes C and D, and glandular trichome B and low density of glandular trichome A) were dominant over the trichome features of C. cajan. A single dominant gene as indicated by the segregation patterns individually will govern each trait in the F₂ and backcross generation. Segregation ratio of 3 (resistant): 1 (susceptible) for resistance to pod borer in the F₂ generation under field conditions was corroborated with a ratio of 1:1 in the backcross generation, and the ratio of 1 non-segregating (resistant): 2 segregating (3 resistant: 1 susceptible): 1 non-segregating (susceptible) in F₃ generation. Similar results were obtained for pod borer resistance under no-choice conditions. Resistance to pod borer and trichomes associated with it (low density of type A trichome and high density of type C) are governed individually by a dominant allele of a single gene in C. scarabaeoides. Following backcrossing, these traits can be transferred from C. scarabaeoides into the cultivated background.     

Inheritance of adult-plant resistance to Phytophthora capsici in pepper

Summary Inheritance studies were conducted to determine the genetic basis of adult-plant resistance in pepper (Capsicum annuum L.) to Phytophthora capsici. F₁, backcrosses and F₂ populations were developed using the resistant parent Criollo de Morellos 334 and susceptible parents Agronômico 10-G and Yolo Wonder. Pepper plants, at 36 days post-emergence, were inoculated near the base of the stem with an inoculum suspension of 5×10⁴ zoospores/ml. Segregation ratios in the F₂ generation of 13 resistant to 3 susceptible plants fit a 2-gene model for resistance with dominant and recessive epistasis.     

The inheritance of resistance to head blight caused by Fusarium culmorum in winter wheat

Summary Crosses were made among ten winter wheat genotypes representing different levels of resistance to Fusarium head blight to obtain F₁ and F₂ generations. Parents, F₁ and F₂ were inoculated with one strain of Fusarium culmorum. Data on incidence of head blight 21 days after first inoculation were analyzed. Broad-sense heritabilities averaged 0.39 and ranged from 0.05 to 0.89 in the individual F₂ families. The joint-scaling test indicated that the inheritance of Fusarium head blight resistance was adequately described by the additive-dominance model, with additive gene action being the most important factor of resistance. With respect to the non-additive effects, dominance of resistance predominated over recessiveness. The number of segregating genes governing resistance in the studied populations was estimated to vary between one and six. It was demonstrated that resistance genes differed between parents and affected resistance differently.     

Inheritance of resistance to fruit rot (Phytophthora capsici Leon.) and induction of resistance in bell pepper (Capsicum annuum L.)

Summary Fruit rot in bell pepper caused by Phytopthora capsici Leon. is a limiting factor in its commercial production. Crosses were made between Waxy Globe, a small fruited hot type, resistant to fruit rot and four highly susceptible bell pepper commercial cultivars (Chinese Giant, California Wonder, Osh, Kosh and Yolo Wonder). Studies of the F₁'s, F₂'s and backcrosses indicated that Waxy Globe carries a dominant gene imparting resistance to fruit rot. After three backcrosses with California Wonder, lines were obtained combining the resistance gene of Waxy Globe with the large fruit size and low capsaicin of California Wonder.     

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.     

Diallel analysis of resistance to head blight caused by Fusarium culmorum in winter wheat

Summary Ten homozygous winter wheat genotypes representing different levels of resistance to Fusarium head blight were crossed in all possible combinations excluding reciprocals. Parents, F₁ and F₂ were inoculated with one pathogenic strain of Fusarium culmorum. Data for head blight, observed 21 days after first inoculation (OBS-2), and for the area under the disease progress curve, based on observations 14, 21 and 28 days after first inoculation (AUDPC), were analyzed. The contrast between parents and F₁ crosses indicated dommance effects of the resistance genes. Diallel analysis according to Griffing's Method 4, Model 1 showed significant general combining ability (GCA) effects for both F₁ and F₂; specific combining ability effects were not significant. With the exception of one genotype for which general performance for Fusarium resistance was not in agreement with its GCA, the resistance to F. culmorum was uniformly transmitted to all offspring, and the parents can be described in terms of GCA. It is suggested that in the progenies with one of the awned lines as parent, one resistance gene was linked with the gene coding for presence of awns, located on chromosome 4B. A single observation date, taken at the right time, was as effective in assessing resistance as the AUDPC.     

Inheritance of anthracnose resistance in the common bean cultivar Widusa

Snap bean (Phaseolus vulgaris L.) cultivar, Widusa, was crossed to Michigan Dark Red Kidney (MDRK), Michelite, BAT 93, Mexico 222, Cornell 49–242, and TO cultivars to study the inheritance of resistance to anthracnose in Widusa. The segregation patterns observed in six F₂ populations supported an expected 3R:1S ratio suggesting that Widusa carries a single dominant gene conditioning resistance to races 7, 65, 73, and 453 of Colletotrichum lindemuthianum, the causal organism of bean anthracnose. Allelism tests conducted with F₂ populations derived from crosses between Widusa and Cornell 49–242 (Co-2), Mexico 222 (Co-3), TO (Co-4), TU (Co-5), AB 136 (Co-6), BAT 93 (Co-9), and Ouro Negro (Co-10), inoculated with races 7, 9, 65 and 73, showed a segregation ratio of 15R:1S. These results suggest that the anthracnose resistance gene in Widusa is independent from the Co-2, Co-3, Co-4,Co-5, Co-6, Co-9, and Co-10 genes. A lack of segregation was observed among 200 F₂ individuals from the cross Widusa/MDRK, and among 138 F₂ individuals from the cross Widusa/Kaboon inoculated with race 65, suggesting that Widusa carries an allele at the Co-1 locus. We propose that the anthracnose resistance allele in Widusa be named Co-1 ⁵ as Widusa exhibits a unique reaction to race 89 compared to other alleles at the Co-1 locus. RAPD marker A18₁₅₀₀ co-segregated in repulsion-phase linkage with the Co-1 ⁵ gene at a distance of 1.2 cM and will provide bean breeders with a ready tool to enhance the use of the Co-1 ⁵ gene in future bean cultivars.     

Effects of resistance genes,heat tolerance genes and cytoplasms on expression of resistance to Pseudomonas solanacearum (E.F. Smith) in potato

Summary Effects of resistance genes and heat tolerance genes on expression of resistance to bacterial wilt caused by Pseudomonas solanacearum were investigated in 30 F₁ progenies from parents with different levels of bacterial wilt resistance and heat tolerance. A race 1 and a race 3 isolate of the bacterium were used for inoculation under screenhouse conditions at two locations. Results obtained indicated that with reduction in levels of parental resistance, resistance in the F₁ progenies was also reduced. Under hot conditions, a reduced heat tolerance in the genetic background also resulted in lower levels of resistance expression. The effect of heat tolerance tended to diminish at lower temperatures leaving the effect of resistance genes more consistent. There existed a strong interaction between resistance genes and genes for heat tolerance. The nature of resistance to bacterial wilt in potato and implications for breeding for resistance are discussed.Effects of reciprocal crosses on expression of resistance to a race 1 isolate under hot screenhouse conditions, were studied in 5 sets of reciprocal F₁ progenies involving different resistant and susceptible parents. The reciprocal differences observed were not significant suggesting absence of cytoplasmic effects on expression of resistance.     

Variation and inheritance of leaf angle, and its association with spot blotch (Bipolaris sorokiniana) severity in wheat (Triticum aestivum)

One thousand four hundred and seven spring wheat germplasm lines belonging to Indian and CIMMYT wheat programs were evaluated for their leaf angle and resistance to spot blotch caused by Bipolaris sorokiniana during three consecutive crop seasons, 1994–95, 1995–96 and 1996–97.Disease severity was recorded at six different growth stages beginning from tillering to late milk stage. Three crosses (M 3109 × Sonalika, HP 1808 × K 9006 and HD 2662 × K 9006) were made between genotypes with erect and drooping leaves. M 3109 was resistant, Sonalika susceptible while the other three lines possessed moderate resistance to spot blotch. Individually threshed F₂ plants were used to advance the generations. Leaf angle and spot blotch resistance were recorded in parents, F₁, F₃, F₄and F₅ generations. Leaf erectness in F₁ generation showed partial dominance. Evaluation of F₃, F₄ and F₅ progenies(120–150) revealed that leaf angle was under the control of few genes that appeared to be close to three. Germplasm lines with erect and semi-erect leaves displayed lower spot blotch severity than those having drooping and semi-drooping leaves. Lines homozygous for erect leaf posture in F₃,F₄ and F₅ generations showed significantly lower mean AUDPC than those with drooping leaves. A positive correlation (0.58) between leaf angle and AUDPC further indicated a positive influence of leaf erectness on severity to spot blotch disease. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic basis of pod borer (Helicoverpa armigera) resistance and grain yield in desi and Kabuli Chickpea (Cicer arietinum L.) under unprotected conditions

A series of half-diallel crosses involving early, medium and late maturity desi and kabuli type chickpea (Cicer arietinum L.) genotypes with stable resistance to Helicoverpa pod borer, along with the parents, were evaluated at two locations in India to understand the inheritance of pod borer resistance and grain yield. Inheritance of resistance to pod borer and grain yield was different in desi and kabuli types. In desi type chickpea, the additive component of genetic variance was important in early maturity and dominance component was predominant in medium maturity group, while in the late maturity group, additive as well as dominance components were equally important in the inheritance of pod borer resistance. Both dominant and recessive genes conferring pod borer resistance seemed equally frequent in the desi type parental lines of medium maturity group. However, dominant genes were in overall excess in the parents of early and late maturity groups. In the kabuli medium maturity group, parents appeared to be genetically similar, possibly due to dispersion of genes conferring pod borer resistance and susceptibility, while their F₁s were significantly different for pod borer damage. The association of genes conferring pod borer resistance and susceptibility in the parents could be attributed to the similarity of parents as well as their F₁s for pod borer damage in kabuli early and late maturity groups. Grain yield was predominantly under the control of dominant gene action irrespective of the maturity groups in desi chickpea. In all the maturity groups, dominant and recessive genes were in equal frequency among the desi parental lines. Dominant genes, which tend to increase or decrease grain yield are more or less present in equal frequency in parents of the early maturity group, while in medium and late maturity groups, they were comparatively in unequal frequency in desi type. Unlike in desi chickpea, differential patterns of genetic components were observed in kabuli chickpea. While the dominant genetic component was important in early and late maturity group, additive gene action was involved in the inheritance of grain yield in medium duration group in kabuli chickpea. The dominant and recessive genes controlling grain yield are asymmetrically distributed in early and medium maturity groups in kabuli chickpea. The implications of the inheritance pattern of pod borer resistance and grain yield are discussed in the context of strategies to enhance pod borer resistance and grain yield in desi and kabuli chickpea cultivars.     

Heterosis in CMS hybrids of cotton for photosynthetic and chlorophyll fluorescence parameters

Summary The characterization of photosynthetic, chlorophyll fluorescence parameters and yield and yield components was compared between two newly developed CMS cotton hybrids (H1, H2) and their parents, as well as currently planted hybrid and conventional cultivars (C1, artificially produced hybrid CCRI 29 and C2, conventional cultivar CCRI 12) under the field condition. The results showed that P_n, F_v/F_m, Φ_PSII and qP of hybrids was significantly higher than that of C1 and C2. Furthermore, heterosis was found on photosynthetic parameters in hybrids over their parents at the first four growth stages, while only heterosis over mean of parents (HOMP) was detected in chlorophyll fluorescence parameters. It was clearly shown that one male-sterile line M2 was higher than the hybrids in F_v/F_m, Φ_PSII and qP over all growth stages. Significantly positive correlations (P < 0.01) were found between LAI or Yield and P_n, C_s, T_r, F_v/F_m, Φ_PSII, or qP, while significantly negative correlations between C_i and LAI or Yield, and no significance between qN and Chl a, C_s and qP were found. It was concluded that CMS hybrid cottons showed better potential to maintain relatively higher photosynthetic ability during the growth, which contributes to the increased lint yield.     

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.     

Inheritance and allelism of resistances to the Russian wheat aphid in seven wheat lines

Summary Studies were conducted to determine the inheritance and allelic relationships of genes controlling resistance to the Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), in seven wheat germplasm lines previously identified as resistant to RWA. The seven resistant lines were crossed to a susceptible wheat cultivar Carson, and three resistant wheats, CORWA1, PI294994 and PI243781, lines carrying the resistance genes Dn4, Dn5 and Dn6, respectively. Seedlings of the parents, F₁ and F₂ were screened for RWA resistance in the greenhouse by artificial infestation. Seedling reactions were evaluated 21 to 28 days after the infestation using a 1 to 9 scale. All the F₁ hybrids had equal or near equal levels of resistance to the resistant parent indicating dominant gene control. Only two distinctive classes were present and no intermediate types were observed in the F₂ segregation suggesting major gene actions. The resistance in PI225262 was controlled by two dominant genes. Resistance in all other lines was controlled by a single dominant gene. KS92WGRC24 appeared to have the same resistance gene as PI243781 and STARS-9302W-sib had a common allele with PI294994. The other lines had genes different from the three known genes.