No abstract

Pod shatter susceptibility was investigated in Brassica napus germplasm and shatter resistant species of B. juncea and Sinapis alba. The comparisons were made by measuring seed yield in field plots, detached pod rupture energy (RE) and the half-life of pod-opening. Pod shatter resistance was significantly greater in B. napus lines derived from interspecific hybridizations of B. napus with B. rapa, B. carinata and B. juncea, than common B. napus cultivars. While these lines exhibited no significant difference in resistance to pod shatter than B. juncea, an entry of S. alba had no yield loss caused by pod shatter. Resistance to pod shatter was characterized in the field as little or no yield loss after full maturity, delayed shattering in time, and stable yield performance under variable climatic conditions during pod maturity. Yield loss caused by pod shatter ranged from a low of 4% for the B. juncea cv. ÔAC VulcanÕ to a high of 61% for the black seeded B. napus line DH12075 in 2-year field trials after 1 month maturity. Pod shatter resistance was not significantly associated with specific plant and pod morphological traits, except pod length (P ¼ 0.005) in tested materials. Field visual scores of pod shatter through inspections of average pod shatter per plant within plots were highly correlated with plot yield loss. Indoor quantitative evaluations of pod strength using a pendulum machine to measure pod RE and random impact test to measure half-life of pod-opening resistance were highly correlated with field yield loss. Multiple evaluations of pod shatter in method and in time after pod maturity are recommended for reliable evaluation of pod shatter resistance.

Embryo reseue teelmiques were used to otitam hybrids between Sinapis alba L. (white mustard) and Brassiea napus F. (oilseed rape) with the goal ot improving the disease toleranee of oilseed rape. Hybrid plants with 31 or 43 ehromosomes were only recovered, when .S. alba was used as the female parent. One hybrid was obtained from the eross S. alba L. ev. 'Kirby' X B. napus F. ev. 'Topas', while 26 hybrids were obtained, when various .S. alba F. eultivars were pollinated with the rapid cycling B. napus line GrGG 5006. All F| hybrid plants were male sterile; however, ttie first generation baekeross to B. napus L., also obtained hy embryo reseue, produeed plants witti 50 ehromosomes and 61-84 "/o potlen viability. Seeond baekeross generation seed was produeed by normal se.xual erossing. Preliminary eytologieal anatyses of potlen mother cells of hybrid plants suggests the possibility ot genetie e.xchange between the two speeies.

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Cultivars in Brassica napus var. oleifera, a self‐pollinating, self‐compatible species, have traditionally been developed as open‐pollinated lines or populations. Significant yield gains in this species have been realized through the exploitation of heterosis. Commercial hybrid production has been possible as a result of the development of a number of pollination control systems. Self‐incompatibility was transferred from B. oleracea var. italica to B. napus var. oleifera through interspecific hybridization. The response to interspecific pollination, as measured by pod elongation and initial stages of ovule development, was genotype dependent, and two highly responsive B. napus genotypes were identified. Embryo rescue was used to produce the interspecific hybrids. Isoelectric focusing of stigma proteins was used to identify S‐alleles in the interspecific hybrids to facilitate backcrossing. Segregation of the S‐locus through a series of back‐crosses to B. napus was complicated by aneuploidy; however, the S‐locus was found to segregate as a single gene. Usefulness of B. oleracea as a source of S‐alleles for pollination control in B. napus is discussed.