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Mycosphaerella blight, caused mainly by Mycosphaerella pinodes (Berk. and Blox.) Vestergren, is the most important foliar disease on field pea (Pisum sativum L.) in western Canada. A quantitative trait analysis of resistance to M. pinodes was undertaken on five crosses with reciprocals of P. sativum to examine broad-sense ([H.sup.2]) and narrow-sense ([h.sup.2]) heritability, minimum number of genes involved (MNG), mid-parent heterosis (MPH), cytoplasmic inheritance, and epistasis. Mean [H.sup.2] was 0.75 (range 0.67-0.80) and mean [h.sup.2] was 0.59 (range 0.41-0.70), indicating that additive variance is important and that improvement in resistance can be achieved through breeding. Mean MNG was 2.16 genes (range 0.06-6.22), indicating that genes for resistance differed among parent lines. Mean MPH was 50% (range 47-57%), indicating that heterosis did not influence the expression of resistance to M. pinodes. There was no difference between the mean of any [F.sub.1] population and its reciprocal, indicating lack of maternal inheritance. The mean of the epistatic points was -0.01 (range -0.1 to 0.12), indicating that epistasis was not important in these crosses. These results will further the understanding of the natural genetic diversity for disease resistance to M. pinodes in P. sativum.

Abstract: Three copies of the gene that encodes cytochrome c oxydase subunit Vb were isolated from the pea (PscoxVb-1, PscoxVb-2, and PscoxVb-3). Northern Blot and reverse transcriptase-PCR analyses suggest that [...]

Comprehensive assessments of germplasm collections of field pea (Pisum sativum L.) have failed to identify any accessions that are highly resistant to Mycosphaerella blight, caused by Mycosphaerella pinodes. In the present study, the broad-sense heritability of resistance to M. pinodes was studied on 558 pea genotypes in a detached-leaf assay and in field trials over 2 yr. in addition, analysis of covariance in disease reaction between the two assessment methods was examined. Only a few genotypes displayed relatively high levels of resistance, and as expected, no complete resistance was observed. The pattern of differences in reaction to M. pinodes among the genotypes demonstrates that resistance is quantitative and moderately heritable. Broad-sense heritability was higher in the detached-leaf assays than in the field trials, likely because of more environmental variance in the field. Covariance between repetitions of the detached leaf assays was not significant but was significant between the field tests. This indicates that detached-leaf assessments are more reliable for assessment of large numbers of accessions.

Sequences flanking 73 insertions of the retrotransposon PDR1 have been characterized, together with an additional 270 flanking regions from one side alone, from a diverse collection of Pisum germ plasm. Most of the identified flanking sequences are repetitious DNAs but more than expected (7%) lie within nuclear gene protein-coding regions. The approximate age of 52 of the PDR1 insertions has been determined by measuring sequence divergence among LTR pairs. These data show that PDR1 transpositions occurred within the last 5 MY, with a peak at 1-2.5 MYA. The insertional polymorphism of 68 insertions has been assessed across 47 selected Pisum accessions, representing the diversity of the genus. None of the insertions are fixed, showing that PDR1 insertions can persist in a polymorphic state for millions of years in Pisum. The insertional polymorphism data have been compared with the age estimations to ask what rules control the proliferation of PDR1 insertions in Pisum. Relatively recent insertions (< ~1.5MYA) tend to be found in small subsets of the Piston accessions set, 'middle-aged' insertions (between ~1.5 and 2.5 MYA) vary greatly in their occurrence, and older insertions (> ~2.5 MYA) are mostly found in small subsets of Pisum. Finally, the average age estimate for PDRI insertions, together with an existing data set for PDR1 retrotransposon SSAP markers, has been used to derive an estimate of the effective population size for Pisum of ~7.5 X [10.sup.5].