Male gametophytic selection in maize

Summary There is evidence that male gametophyte selection is a widespread phenomenon in higher plants. The pollen tube growth rate is one of the main components of gametophyte selective value; genetic variability for this trait, due to the effect of single genes or to quantitative variation, has been described in maize. However, indication of gametophytic selection has been indirectly obtained; its effect was revealed by the positive relation observed between gametophyte competitive ability and sporophyte metrical traits.This paper considers the results of selection applied to gametophyte populations produced from single plants. The competitive ability of the lines was evaluated in comparison with that of a standard line by means of the pollen mixture technique. Sporophytic traits were measured in the hybrid progeny obtained by crossing selected S₃ and S₄ families with an unrelated single cross and an inbred line. Gametophyte selection produced inbred lines with high gametophyte competitive ability. In view of the selection procedure adopted, this result was interpreted as an indication of haploid expression of genes involved in the control of pollen tube growth. Moreover, this gametophytic trait was positively correlated with sporophytic traits (seedling weight, kernel weight and root tip growth in vitro), indicating that both groups of characters have a common genetic basis.     

Development of chickpea near-isogenic lines for fusarium wilt

Four pairs of near-isogenic lines (NILs) of chickpea with resistance/susceptibility to Fusarium oxysporum f. sp. ciceris (Foc) have been developed in this study. These lines were produced by searching in advanced recombinant inbred lines (RILs) that are segregating for Foc race 5 based on a phenotypic screening. The sequence tagged microsatellite (STMS) marker TA59, closely linked to wilt resistance genes on linkage group 2 (LG2) of the chickpea map, was used to assist the selection of resistant or susceptible genotypes. The NILs were also characterized for disease reaction to Foc races 1A, 2, 3 and 4. Resistance, susceptibility and slow wilting reactions were found in these NILs. Our results suggest that more than one gene controls the resistance to race 5. Combination of the major gene foc-5 linked to TA59 with other gene/s appears to be required to complete resistance, and the absence of these unknown genes leads to slow wilting reactions. The independent differential responses to races 2 and 3 observed in three NILs could be explained as recombination events. This result suggests that foc-2 and foc-3 are delimiting points at opposite ends of a genomic region that includes the remaining foc genes and the TA59 marker. This set of NILs has great potential for studying the genetics and mechanisms of wilt resistance. In addition, the NIL RIP8-94-11 can be used as differential line for Foc race 3; it showed a clear resistance reaction to race 3 and susceptibility to the other Foc races.     

Molecular mapping of wilt resistance genes in chickpea

Fusarium wilt is a widespread and serious chickpea disease caused by the soil-borne fungus Fusarium oxysporum f.sp. ciceri (Foc). We evaluated an F₉ recombinant inbred line population of chickpea for resistance to three Foc races (1, 2 and 3) in pot culture experiments and identified flanking and tightly linked DNA markers for the resistance genes. The simple sequence repeat markers H3A12 and TA110 flanked the Foc1 locus at 3.9 and 2.1 cM, respectively, while Foc2 was mapped 0.2 cM from TA96 and 2.7 cM from H3A12. The H1B06y and TA194 markers flanked the Foc3 locus at 0.2 and 0.7 cM, respectively. These markers were also validated using 16 diverse chickpea genotypes. Identification of tightly linked flanking markers for wilt resistance genes will be useful for their exploitation in breeding programs and to understand the mechanism of resistance and evolution of the genes. S. J. M. Gowda and P. Radhika contributed equally to this study.     

Marker Assisted Selection (MAS) for chickpea Fusarium oxysporum wilt resistant genotypes using PCR based molecular markers

The exploration of genetically superior accessions is the key source of germplasm conservation and potential breeding material for the future. To meet the demand of better yielding chickpea cultivars in Pakistan the present study was organized to select more stable and resistant lines from indigenous as well as exotic chickpea germplasm obtained from Plant Genetic Resource Institute (PGRI), National Agricultural Research Centre, Islamabad, Pakistan. For the identification and evaluation of chickpea wilt resistant lines against Fusarium oxysporum f. sp. ciceris (Schlechtends), the germplasm was tested in the field for the selection of wilt resistant lines and the PCR based molecular markers were investigated to use Marker Assisted Selection (MAS) for selection of the desirable cultivars. In field trial, 70 % accessions were resistant to wilt disease, while the remaining 30 % have shown susceptibility to the disease. A total of 5 RAPD and 15 SSR markers were screened for molecular based characterization of wilt response. The data of molecular markers were scored by the presence (1) and absence (0) of allele and subjected to statistical analysis. The analysis was based on coefficient of molecular similarity using UPGMA and sorted the germplasm into two groups based on disease response. Among the total used RAPD/SSR primers, only TA194 SSR marker showed linkage to wilt resistant locus at 85 % probability. The linkage of a marker was reconfirmed by receiver operating characteristic curve. The use of the sorted wilt resistant genotypes through SSR marker TA194 can make available ample prospect in MAS breeding for yield improvement of the crop in Pakistan.     

Genetic variability of Fusarium wilt pathogen isolates of chickpea (Cicer arietinum L.) assessed by molecular markers

Genetic variability among 43 isolates of Fusarium oxysporum f.sp. ciceri, the chickpea wilt pathogen, collected from nine states of India including the four well-characterized races of the pathogen were assessed using the molecular markers, RAPDs and AFLP. Principal coordinate analysis of the similarity index data generated from the molecular marker studies mostly gave three different clusters: Of these two clusters represented race-1 and race-2, and the third cluster consisted of race-3 and race-4 pathogen isolates. In RAPDs a fourth cluster was seen which did not go with any of the four races of the pathogen. The molecular markers established the distinctness of race-1 and race-2 pathogen isolates and the close similarity of pathogen isolates of race-3 with that of race-4. AFLP was found to be more informative as it differentiated more number of the pathogen isolates with the known races with minimum of outliers. The high levels of DNA polymorphism observed with the molecular markers suggest the rapid evolution of new recombinants of the pathogen in the chickpea growing fields. This revised version was published online in June 2006 with corrections to the Cover Date.     

Genetic analysis of agronomic characters in chickpea

Summary Twenty-eight diallel trials over 8 years and two locations were analysed to estimate genetic variances for agronomic characters of chickpea (Cicer arietinum L.). The data were analysed according to Method 4 and Model I of Griffing (1956). Days to flowering, plant height, and seed size were found to be predominantly under additive inheritance and were highly predictable. Both additive and non-additive genetic components were important for seed yield, number of branches, pods per plant, and seeds per pod. Although both general combining ability (gca) and specific combining ability (sca) varied significantly with generation, components of gca mean squares were invariably much larger than gca x generation interaction components, indicating that either the F₁ or the F₂ generation can be used to estimate the gca components effectively. Combined diallel analysis of F₂s over locations revealed the importance of combining ability x location interactions and emphasized the need for testing over more than one location for the precise estimation of combining ability. The implications of these findings and those reported earlier in the literature on the breeding strategies/methods for the genetic improvement of agronomic characters in chickpea are discussed.ICRISAT journal article no. 1199     

Induction of systemic resistance in chickpea against Fusarium wilt by Bacillus strains

Plant growth promoting rhizobacteria (PGPR) strains Rb29 (B. amyloliquefaciens MF352007), Bs1 (B. subtilis MF352017) and Bt1 (B. tequilensis MF352019) were tested for growth promotion and for their ability to induce systemic resistance against Fusarium wilt, a vascular disease of chickpea, using two methods that include whole plant and a split-root system. Bacillus strains and Fusarium oxysporum f. sp. ciceris (FOC) were inoculated on separate halves of roots of chickpea seedlings at the same time and then planted in separate pots either in superposition or one side of the other. All Bacillus strains systemically induced resistance against FOC, and significantly (p < 0.05) reduced the wilt disease by 98–100%. Application of Bacillus strains effectively enhanced plant growth, leading to increased plant height, root length, a fresh and dry weight of shoots and roots. These results help to explain the role of strains of Bacillus in growth promotion and biological control of Fusarium wilt in chickpea. This is the first report of systemic-induced resistance against Fusarium wilt in chickpea obtained by application of Bacillus strains to a root system spatially separated from the FOC-inoculated root.     

Genetic parameters and selection strategies for soybean genotypes resistant to the stink bug-complex

Soybean genotypes resistant to stink bugs are derived from complex breeding processes obtained through indirect selection. The aim of the present work was to estimate genetic parameters for guiding selection strategies towards resistant genotypes, based on those traits associated with responses to pod-attacking stink bugs, such as the grain filling period (GFP), leaf retention (LR), percentage index of pod damage (PIPD) and percentage of spotted seeds (PSS). We assessed the parental lines IAC-100 (resistant) and FT-Estrela (susceptible), the progenies F(2) and F (4) , 30 progenies F (2:3) , 30 progenies BC (1) F (2:3) and 30 progenies BC (2) F (2:3) , besides the cultivars BRS Celeste and MGBR-46 (Conquista). Three field experiments, using randomized complete block design with three replications, were installed in Goiania-GO, in the 2002/03 season. Each experiment consisted of 36 treatments (6 common and 30 regular). Heritability estimates were: 74.6 and 36.1 (GFP); 51.9 and 19.9 (LR); 49.6 and 49.6 (PIPD) and 55.8 and 20.3 (PSS), in both the broad and narrow senses, respectively. Based on these results, we concluded that the best strategy for obtaining stink bug-resistant genotypes consists of selecting the PIPD trait in early generations (F (3) or F (4) ), followed by selection for the GFP, LR and PSS traits in generations with higher endogamy levels.     

In vitro selection for Fusarium wilt resistance in Gladiolus

Cormels pieces of four Fusarium susceptible Gladiolus cultivara (Friendship, Peter Pears, Victor Borge and Novalux) formed friable calli when cultured in vitro on Murashige and Skoog basal medium containing various concentrations of auxin and cytokinin. The friable calli established cell suspensions. Plantlet regeneration was obtained from the control callus, control cell suspension derived callus and in vitro selected Fusarium oxysporum Schlecht. resistant cell-lines of Friendship. The in vitro cormlets showed 85-95% germination after breaking dormancy of 8weeks at 4℃. Cell suspensions of all four Gladiolus cultivara were found to be highly sensitive to fusaric acid. Gradual Increase in fusaric acid concentrations to the cell-suspension cultures decreased cell growth considerably. One albino plant was found from the second generation of the In vitro selected cell line of Friendship. The albino plant was found to be highly susceptible to F. oxysporum. The cormlets of all in vitro selected call lines of Friendship were inoculated with a conidial suspension of the F. oxysporum before planting and were also sprayed with the same spore suspension for further characterization when the height of plants was about 6cm. The four selected cell lines showed the same response whether or not they were Inoculated with conidia of the F. oxysporum. Plantlets of all of the selected call lines exhibited significant growth as compared with the control after application of conidia of the F.oxysporum.     

广藿香抗青枯病离体筛选技术的研究

以广藿香叶片及带节茎为材料,研究青枯菌粗毒素不同制备方法、青枯菌不同培养时间及不同菌液浓度对外植体离体再生的影响。结果表明:过滤灭菌法制备的青枯菌粗毒素致毒性比湿热灭菌法处理更强,外植体成活率明显降低;以培养12 h的青枯菌粗毒素对外植体有较大的致毒性,外植体变褐死亡现象较突出,培养30 d后,叶片及带节茎出芽率分别为10.33%及36.11%;浓度在1.41×10~8 cfu/ml以上的菌液粗毒素对外植体有明显的毒害作用,大多外植体枯黑死亡,出芽率较低,同时在该浓度时,大多数无根苗难以生根,植株基部变黑,叶片变黄,生长不良。确定了青枯菌粗毒素对广藿香不同离体培养阶段的致毒性,建立了以青枯菌粗毒素为选择压力的广藿香离体筛选体系。     

Sporophytic recognition of pollen S alleles in the gametophytic self-incompatibility system of Nemesia strumosa benth

Summary Several seedlings of Nemesia strumosa with various levels of pseudo-self-compatibility (PSC) often produced more seed after self pollination than when pollinated using pollen from incompatible plants bearing the same S alleles. Sporophytic recognition of self pollen apparently increases PSC levels above those attributable to modifying genes which interfere with normal stylar activity.Scientific Journal Series Paper Number 9546 of the Minnesota Agricultural Experiment Station.     

Biological control of chickpea Fusarium wilt by antagonistic bacteria under greenhouse condition

In this survey, Fusarium oxysporum was isolated from roots infected plants and was shown to be pathogenic. Experiment were carried out with seven antagonistic bacteria. Based on biochemical, Physiological and morphological tests, isolates B-120, B-32, B-28 and B-22 were identified as Bacillus subtilis and isolates Pf-100, Pf-10 and CHAO as Pseudomonas fluorescens. In greenhouse studies, only isolate B-120 (Less than benomyl) reduced Fusarium wilt of chickpea in both seed and soil treatments. The application of antagonistic bacteria had no different effects on plant growth factors. Soil treatment of bacteria had a better effects on plant growth than that of bacterial seed treatment. The use of antagonists (B-120, B-28, B-120 and CHAO) in combination had no significant effect on plant growth factors and reduction wilt disease than that each isolate was applied individually.     

Inheritance of inter-simple-sequence-repeat polymorphisms and linkage with a fusarium wilt resistance gene in chickpea

 The inheritance of an inter-simple-sequence-repeat (ISSR) polymorphism was studied in a cross of cultivated chickpea (Cicer arietinum L.) and a closely related wild species (C. reticulatum Lad.) using primers that anneal to a simple repeat of various lengths, sequences and non-repetitive motifs. Dinucleotides were the majority of those tested, and provided all of the useful banding patterns. The ISSR loci showed virtually complete agreement with expected Mendelian ratios. Twenty two primers were used for analysis and yielded a total of 31 segregating loci. Primers based on (GA)_n repeats were the most abundant while primers with a (TG)_n repeat gave the largest number of polymorphic loci. Nucleotides at the 5′ and 3′ end of the primers played an important role in detecting polymorphism. All the markers showed dominance. We found an ISSR marker linked to the gene for resistance to fusarium wilt race 4. The marker concerned, UBC-855₅₀₀, was found to be linked in repulsion with the fusarium wilt resistance gene at a distance of 5.2 cM. It co-segregated with CS-27₇₀₀, a RAPD marker previously shown to be linked to the gene for resistance to fusarium wilt race 1, and was mapped to linkage group 6 of the Cicer genome. This indicated that genes for resistance to fusarium wilt races 1 and 4 are closely linked. The marker UBC-855₅₀₀ is located 0.6 cM from CS-27₇₀₀ and is present on the same side of the wilt resistance gene. To our knowledge this is the first report of the utility of an ISSR marker in gene tagging. These markers may provide valuable information for the development of sequence-tagged microsatellite sites (STMS) at a desired locus. Received: 10 August 1997 / Accepted: 6 October 1997     

Variability in Fusarium oxysporum f. sp. ciceri causing vascular wilt in chickpea

The variability in cultural characteristics and the virulence among three isolates of Fusarium oxysporum f. sp. ciceri causing vascular wilt in chickpea was studied under laboratory conditions. The three isolates (Foc-1, Foc-2 and Foc-3) did not show any significant difference in their mycelial dry weight production at any temperature regimes, pH level or the growth media tested. The radial growth on PDA also did not differ significantly in the three isolates. However, some quantitative differences were noted in colony characters and septations in macroconidia of these isolates. The isolate Foc-1 exhibited dull white, thin and flat hairy growth, spreading out like thread, Foc-2 showed a white fluffy colony with irregular aerial margin, while Foc-3 exhibited a pinkish white, slightly fluffy colony with regular margin. Conidia also differed with regard to septation. Three to six septa were present in Foc-2, while there were 2–3 in isolates Foc-1 and Foc-2. These isolates differed significantly with regard to their virulence on test varieties. Isolate Foc-1 was more virulent that Foc-2 or Foc-3 and produced abundant spores.     

Genetic dissection of photosynthetic efficiency traits for enhancing seed yield in chickpea

Understanding the genetic basis of photosynthetic efficiency (PE) contributing to enhanced seed yield per plant (SYP) is vital for genomics‐assisted crop improvement of chickpea. The current study employed an integrated genomic strategy involving photosynthesis pathway gene‐based association mapping, genome‐wide association study, quantitative trait loci (QTL) mapping, and expression profiling. This identified 16 potential single nucleotide polymorphism loci linked to major QTLs underlying 16 candidate genes significantly associated with PE and SYP traits in chickpea. The allelic variants were tightly linked to positively interacting QTLs regulating both enhanced PE and SYP traits as exemplified by a chlorophyll A‐B binding protein‐coding gene. The leaf tissue‐specific pronounced up‐regulated expression of 16 associated genes in germplasm accessions and homozygous individuals of mapping population was evident. Such combinatorial genomic strategy coupled with gene haplotype‐specific association and in silico protein–protein interaction study delineated natural alleles and superior haplotypes from a chlorophyll A‐B binding (CAB) protein‐coding gene and its interacting gene, Timing of CAB Expression 1 (TOC1), which appear to be most promising candidates in modulating chickpea PE and SYP traits. These functionally pertinent molecular signatures identified have efficacy to drive marker‐assisted selection for developing PE‐enriched cultivars with high seed yield in chickpea.