Production and characterization of hybrids between Cajanus cajan × C. reticulatus var. grandifolius

Cajanus reticulatus var. grandifolius, endemic to Australia and a wild relative of the cultivated species, C. cajan, was successfully crossed with the latter as the female parent. The major wild species characters such as persistent stipules, long pod hairs, pod shattering, brown seeds with grey speckles, and presence of seed strophiole were dominant in the hybrid. For growth and branching habit, and leaflet, flower, pod, and seed size, the hybrid was intermediate between the parents. The meiotic cells of the hybrid were found to have quadrivalents, trivalents, univalents,and showed reduced chromosome pairing as revealed by the increased number of rod bivalents per cell at metaphase-I, and stickiness and precocious movement of chromosomes to poles in the second division. In comparison to the parents, the hybrid had fewer pods and seeds. However,these anomalies in the interspecific hybrid are not significant enough to preclude the gene transfer from C. reticulatus to the cultivated species through a sexual route. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pattern analysis of genotype × environment interaction for striga resistance and grain yield in African sorghum trials

The parasitic weed Striga hermonthica (Del.) Benth. seriously limits sorghum [Sorghum bicolor (L.) Moench] production in Sub-Saharan Africa. As an outbreeder, S. hermonthica is highly variable with an extraordinary capacity to adapt to different hosts and environments, thereby complicating resistance breeding. To study genotype x environment (G x E) interaction for striga resistance and grain yield, nine sorghum lines, 36 F₂ populations and five local checks were grown under striga infestation at two locations in both Mali and Kenya. Mean squares due to genotypes and G x E interaction were highly significant for both sorghum grain yield and area under striga severity progress curve(ASVPC, a measure of striga emergence and vigor throughout the season). For grain yield, the entry x location-within-country interaction explained most of the total G x E while for ASVPC, entry x country and entry x location-within-country interactions were equally important. Pattern analysis (classification and ordination techniques) was applied to the environment-standardized matrix of entry x environment means. The classification clearly distinguished Malian from Kenyan locations for ASVPC, but not for grain yield. Performance plots for different entry groups showed differing patterns of adaptation. The ordination biplot underlined the importance of entry x country interaction for ASVPC. The F₂ derived from the cross of the striga-resistant line Framida with the striga-tolerant cultivar Seredo was the superior entry for both grain yield and ASVPC, underlining the importance of combining resistance with tolerance in striga resistance breeding. The observed entry x country interaction for ASVPC may be due to the entries' different reactions to climatic conditions and putative differences in striga virulence in Mali and Kenya. This revised version was published online in August 2006 with corrections to the Cover Date.     

Apomictic frequency in sorghum R473

Summary Apomixis has been reported in a few lines of sorghum, among them R473 which was originally reported to be an obligate apomict. Although this line has multiple embryo sacs, the frequency of apomictic seed formation has not been determined because a progeny test has not been possible. R473 does not cross as a female with other lines except when its own pollen is present. In the present study mutations were induced in R473 by hydrazine and irradiation. Crosses were made between male-sterile mutants as females and normal R473 as males. Plants of R473 produced F₁ hybrids sexually, thus indicating that they were not obligate apomicts. These F₁'s also reproduced sexually, as indicated by segregation for male sterility and male fertility in F₂ progenies.     

Species affinities between Cajanus cajan and some Atylosia species based on esterase isoenzymes

Summary Esterase isozymes were studied in seed extracts of Cajanus cajan and six Atylosia species by polyacrylamide gel electrophoresis and isoelectrofocusing. The isozyme patterns were stable and accession specific. Within the accessions of the Atylosia species, A. albicans and A. scarabaeoides showed three common bands indicating that they are more closely related to each other than to the other species. Of the accessions of Atylosia only A. cajanifolia shares the esterase isozyme of C. cajan and hence seems to be the closest wild relative of C. cajan.     

Screening sorghum genotypes for salinity tolerant biomass production

Genetic improvement of salt tolerance is of high importance due to the extent and the constant increase in salt affected areas. Sorghum [Sorghum bicolor (L.) Moench] has been considered relatively more salt tolerant than maize and has the potential as a grain and fodder crop for salt affected areas. One hundred sorghum genotypes were screened for salinity tolerance in pots containing Alfisol and initially irrigated with a 250-mM NaCl solution in a randomized block design with three replications. Subsequently 46 selected genotypes were assessed in a second trial to confirm their responses to salinity. Substantial variation in shoot biomass ratio was identified among the genotypes. The performance of genotypes was consistent across experiments. Seven salinity tolerant and ten salinity sensitive genotypes are reported. Relative shoot lengths of seedlings were genetically correlated to the shoot biomass ratios at all stages of sampling though the relationships were not close enough to use the trait as a selection criterion. In general, the whole-plant tolerance to salinity resulted in reduced shoot Na⁺ concentration. The K⁺/Na⁺ and Ca²⁺/Na⁺ ratios were also positively related to tolerance but with a lesser r ². Therefore, it is concluded that genotypic diversity exists for salt tolerance biomass production and that Na⁺ exclusion from the shoot may be a major mechanism involved in that tolerance.     

Introgression of a gene for delayed pigment gland morphogenesis from Gossypium bickii into upland cotton

The presence of gossypol and its derivatives above the WHO/FAO standards (0.02–0.04%) in cotton seed oil and meal limits its usage as food and feed. To the contrary, the presence of pigment glands filled with gossypol and its derivatives helps to protect cotton plants from phytophageous pests. Thus a desirable cultivar would have glandless seeds on a glanded plant. This paper describes results on the successful introgression of this trait from Gossypium bickii into cultivated upland cotton. Five different tri‐specific hybrids (ABH1, ABH2, ABH3, ABH4 and ABH5) were obtained by crossing the amphidiploid F₁ (G. arboreum × G. bickii) with different gland genotypes of G. hirsutum as male parent. The hybrids were highly sterile, and their chromosome configuration at meiosis metaphase 1 (M1) in pollen mother cell (PMC) was 2n = 52 = 41.04 I + 4.54 II + 0.57 III + 0.04 IV. All five hybrids were similar in morphological characters, except for the gland expression and gossypol contents. The hybrid (ABH3) derived from genotype Gl₂Gl₂gl₃gl₃ of upland cotton (a single gene dominant line) had completely introgressed the target trait of G. bickii. While ABH1 and ABH2, which derived from recessive (gl₂gl₂gl₃gl₃) or dominant (GlGl) glandless upland cotton genotypes, had glandless seeds too, but the density and size of the glands on the plant were reduced significantly.     

Simple sequence repeats as useful resources to study transcribed genes of cotton

Microsatellites or Simple Sequence Repeats(SSRs) are informative molecular genetic markers in many crop species. SSRs are PCR-based, highly polymorphic, abundant, widely distributed throughout the genome and inherited in a co-dominant manner in most cases. Here we describe the presence of SSRs in cDNAs of cotton. Thirty one SSR primer pairs of 220 (∼14%) tested led to PCR amplification of discrete fragments using cotton leaf cDNA as template. Sequence analysis showed 25% of 24randomly selected cDNA clones amplified with different SSR primer pairs contained repeat motifs. We further showed that sequences from the SSR-containing cDNAs were conserved across G. barbadense and G. hirsutum, revealing the importance of the SSR markers for comparative mapping of transcribed genes. Data mining for plant SSR-ESTs from the publicly available databases identified SSRs motifs in many plant species,including cotton, in a range of 1.1 to4.8% of the submitted ESTs for a given species. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic basis of plant regeneration in hexaploid triticale

Summary Glume cultures of monogenic recessive mutants PGTSLS1 (Plant Genetics triticale selection large spike 1) and PGTSLG2 (Plant Genetics triticale selection long grain 2) were employed along with their parent PGTS control (Plant Genetics triticale selection control) and their F1 and F2 progenies, to determine the genetic basis of plant regeneration in hexaploid triticale. The mutant PGTSLS1 exhibited greater efficiency of plant regeneration (22.4%) followed by PGTS control (7.6%) and PGTSLG2 did not exhibit any regeneration. All the three F1's exhibited plant regeneration frequency on par with that of control (6.9–7.3%), suggesting dominant nature of control genotype over the isogenic mutants. The F2 results suggested that genetic control over the high frequency regeneration of PGTSLS1 was monogenic recessive in nature, and genetic control over the recalcitrant nature of PGTSLG2 also was monogenic recessive. The F2 of the cross PGTSLS1 × PGTSLG2 segregated into four classes. Of the 114 F2 plants, 19 showed no regeneration, 70 of them exhibited 6–8% regeneration, 20 of them 19–24% regeneration, and 5 of them exhibited highest frequency regeneration (57–60%). These observations suggest dihybrid segregation for regeneration. The highest frequency of plant regeneration (57–60%) exhibited by 5 F2 plants may be due to the interaction of non-allelic genes in recessive condition. These results clearly demonstrate the association of at least two genes with plant regeneration in hexaploid triticale.