Inheritance of photo-sensitivity in pigeonpea

Pigeonpea [Cajanus cajan (L.) Millsp.] is a short-day legume species and the late maturing genotypes are more photosensitive than early types. To generate information about the inheritance of photo-sensitivity, this study was conducted under natural and artificially extended (16 h) photo-periods using F1, F2 and BC1F1 generations. Under natural photo-period, F1 hybrids showed partial dominance of earliness; while in F2, a normal distribution that was skewed towards earliness was observed. In contrast under extended photo-period, the spread of F2 data was wide with discontinuities recorded at day 70, 82 and 103. Chisquare tests, when applied to F2 and BC1F1 data, suggested that three dominant genes (PS3, PS2 and PS1) controlled the expression of photo-sensitivity. These genes were found operating in a hierarchical order with PS2 and PS1 genes failing to express in the presence of PS3 gene. Similarly in the absence of PS3 gene, PS2 expressed but it masked the expression of PS1. Further, PS1 gene expressed only when both PS3 and PS2 were in recessive homozygous state. Hence, the proposed genetic model for photosensitivity in pigeonpea is PS3 > PS2 > PS1 and photoinsensitive genotype being a triple recessive (ps3ps3ps2 ps2ps1ps1)

Resistance of soybean to rust in Australia

Previously no immunity or high degree of resistance to soybean rust has been reported. The tests described have demonstrated that strong resistance to rust does exist in soybean genotypes, and in particular in one accession of P1200492 (Q12956) and the cultivars derived from it (Tainung 3 and Tainung 4) and in lines P1227268, PI227687 and HY2217. However, these resistances may not be effective against the whole rust population, as evidenced by the identification of a second race of rust which is virulent on the previously immune line P1200492. Rust of soybeans, caused by Phakopsora pachyrhizi Syd., is reported to be widely distributed throughout Asia from China south to Australia (1, 6, 10). The rust causes premature defoliation of plants, with a subsequent increase in the numbers of unfilled pods per plant. Disease loss has not been accurately determined, but the data available show that this disease can cause serious yield loss. In Taiwan it is estimated that, due to rust, production is reduced by 20-30% (8), whilst in individual fields as much as 70-80% of potential yield may be lost (4). In Japan, losses of 15-40% in individual fields are reported (7), and in Thailand losses are estimated to range from 10-30% in individual fields (8). No accurate measures of yield loss have been reported for Australian crops. Screening tests of soybean accessions have been carried out in several countries where the rust is indigenous, to identify sources of resistance to rust. The tests have shown that accessions differ in the severity of rust development that occurs on them, and show varying amounts of field resistance. However, no soybean lines which are immune to the rust, or which show a high degree of resistance have been reported (1). Accession P1200492 (a) was shown to have a high degree of field resistance to rust when tested in Taiwan (2, 3), though it was infected and sporulation occurred readily in glasshouse tests made in the U.S.A. using a Taiwanese isolate (9). PI200492 was used subsequently as a parent to breed cultivars Tainung 3 and Tainung 4 which showed degrees of rust resistance in Taiwan (2, 3

Histological studies of the pre-penetration development and penetration of soybeans by rust, Phakopsora pachyrhizi syd.

Comparisons were made between susceptible, resistant and highly resistant soybean lines of pre-penetration development and penetration of uredospores of rust, Phakopsora pachyrhizi, at intervals after inoculation. Differences between lines were found in the percentage of uredospores which germinated on leaves, and smaller differences were found between lines in appressorium formation and penetration from germinated uredospores. The differences between lines were not related to infection type

Effect of rust (Phakopsora pachyrhizi) on soybean yield and quality in south-eastern Queensland

In a field trial conducted at the University of Queensland Research Farm, Redland Bay in 1976, plots of soybeans were protected from rust, Phakopsora pachyrhizi, with mancozeb sprays for varying periods after sowing. Seed yield losses were 60-70% in the most severely rusted plots. In a glasshouse trial, rust inoculations were commenced at regular intervals during growth, and yield was reduced by 95% in plants inoculated immediately prior to flowering. In both trials, reduced yield was associated with reductions in the number of filled pods per plant, the number of filled seeds per plant and seed weight. The oil but not the protein content of the seed was also reduced in the more severely rusted treatments in the field trial

Inversion heterozygosity in the hybrid soybean × Glycine soja: Evidence from a pachytene loop configuration and other meiotic irregularities

Meiotic irregularities and partial sterility were found in the hybrid between the soybean, Glycine max and its presumed wild progenitor, Glycine soja. Chromosome bridges and fragments were believed to be caused by inversion heterozygosity. The presence of an inversion was confirmed by finding an inversion loop at pachytene. Other evidence for inversions came from bivalents that failed to separate in the first division. These bivalents acted as laggards or passed intact to one pole at anaphase I. Nondisjunction of the partners in the bivalents was believed to result from chiasmata occurring in the region of an inversion in the bivalents. The number of bridges, fragments, and lagging bivalents suggest the presence of more than two inversion differences between the two species.Chromosomal differentiation together with wide genetical and morphological differences provide evidence that G. max and G .soja are two distinctly separate species

Two-way pattern analysis of a large data set to evaluate genotypic adaptation

A method for the analysis of genotype x environment interaction in large data sets is presented and applied to yield data for 49 wheat cultivars grown in each of 63 international environments. Pattern analysis using numerical classification defined separately groups of cultivars and groups of environments, based on similarities in yield performance. The group structure for cultivars was interpreted in terms of similarities and differences in cultivar mean yield and/or cultivar yield response patterns across environments. In addition, the cultivar groups reflected differences in genetical and selectional origin. Environment groups largely reflected differences in the average mean yield of the set of cultivars, but some groups showed differences in response patterns related to differential rust incidence

Pachytene chromosome identification by a key based on chromomeres in the pigeonpea

A method for the preparation and utilization of the pachytene chromosome karyotype of the pigeonpea is presented. Major chromomeres, most of which were compound structures, were used to characterize individual chromosomes. The karyotype was prepared from a large number of cells showing only one or a few analyzable chromosomes, rather than scarce cells showing the entire chromosome complement. As all 11 chromomere patterns were identified in each of two cells showing all 11 chromosomes clearly, this indicated that the entire genome had been described. A key, based on distribution and structure of major chromomeres, provides a rapid means of identification and comparison