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- Author or Editor: Michael H. Dickson x
Abstract
Quality is rather nebulous and often difficult to measure objectively. This is not surprising since edible quality comprises a number of attributes, both physical and chemical. Some of the components of quality have been measured objectively for a long time; others, such as flavor and aroma, have only recently been measured objectively. Previously they were, and in most cases they still are, subject to personal preferences and prejudices.
More than 700 accessions of Brassica vegetables were screened for resistance to bacterial (Erwinia) soft rot disease using a newly developed testing procedure. Dipping a needle in 2-day-old bacterial culture and pricking petioles of plants gave the most-consistent and distinguishable results in both seedling greenhouse and mature plant field tests. High humidity (100%) and warm temperature (higher than 23°C) are the two essential conditions for this test to be successful. So far, immune material has not been found. In B. rapa, less than 7% of the accessions showed some degree of resistance. High correlation was found between seedling greenhouse tests and mature plant field tests. Genetic study showed that soft rot resistance in B. rapa is a quantitative trait. The broad-sense heritability was 60% and narrow-sense heritability was 42% in the tested population. Following three cycles of recurrent selection, the resistance level in cycle three population was improved by 2.4 disease score points (1–9 scale) compared to the original parental population and the disease score of the best line in cycle 3 was 2.7 compared to a susceptible check on which the disease score was 8 under greenhouse conditions. Under field conditions, the best cycle three line scored 2.0 in comparison to the susceptible check, which scored 7. From our study, the recurrent selection works well for improving the resistance level to the soft rot disease in B. rapa.
Abstract
The orange curd mutant in cauliflower (Brassica oleracea L. var. botrytis) Snowball’ (1). Orange curd was controlled by a single dominant gene, or, but the intensity of orange color varied in homozygous (OrOr) and heterzygous (Oror) plants, due to modifying genes. Curd of OrOr plants were generally more intense colored than curds of Oror plants. The OrOr plants are stunted, and produce small curds, ≈30 to 40 mm or less in diameter, compared to Oror or oror curd plants, which have curds 150 to 200 mm in diameter.
Cold-tolerant, Ogura male-sterile, somatic hybrid rapeseed (Brassica napus L.) lines were used as maternal parents in two independent introgression experiments. In one experiment, an atrazine-sensitive B. napus (aacc) somatic hybrid was crossed directly with a male-fertile pak choi (B. campestris Chinensis Group, aa) accession. Allotriploid (sac) progeny were then backcrossed to the recurrent pak choi parent. Forty-five percent of the progeny from the first backcross were determined to be diploids (aa). In the other experiment, an atrazine-resistant B. napus somatic hybrid was crossed first to a bridge line. Three additional backcross generations to Chinese cabbage (B. campestris Pekinensis Group) resulted in Chinese cabbage resistant to black rot (Xanthomonas campestris pv. campestris). These materials may be useful for production of B. campestris hybrid vegetable seed.