Study of Brassica rapa core collection for morphological traits, self-incompatibility, interspecific hybridization and Xanthomonas campestris PV. campestris disease resistance

Mestrado em Engenharia Agronómica - Instituto Superior de Agronomia

Rijk Zwaan Brassica rapa Gene Bank Collection, comprising 137 accessions representing different morphortypes, was studied and evaluated for morphological traits and self incompatibility, interspecific hybridization and Xanthomonas campestris pv. campestris disease resistance. In order to distinguish different morphotypes, leaf and seed pod traits were measured and analized. Only the leaf traits contribute to distinguish between the morphotypes. Recurring to open flowers pollination, self incompatibility was scored through two different methods: assessment of pollen ingrowth and seed counting. Through the assessment of pollen tube ingrowth was concluded that the majority of accessions are self incompatible or moderately self incompatible. Although seed counting does not agree with these results. Success rate of natural interspecific hybridization with Brassica oleracea was accessed through pollination of immature flower buds. Direct and reciprocal pollinations were performed but only the direct pollinations were scored. After counting the seeds it was concluded that success rate was very low. There was no significant correlation between the seed set and plant morphotypes. A screening for resistance against two races (1 and 4) of Xanthomonas campestris pv. campestris was performed. Resistant plants were found for both races. Significant differences in resistance were found for the two races and between morphotypes. Chromossome counting was performed for one accession resistant to both races. After counting it was concluded that it is an allotetraploid, either Brassica carinata (BC) or Brassica juncea (AB), in agreement with the literature, which refers B genome as a resistant. This work was useful to identify the presence of resistance to Xanthomonas campestris pv. campestris race 4 in Brassica rapa. Further work has to be performed to study the nature of the resistance and a larger number of Brassica rapa accessions can still be screened for resistance to Xanthomonas campestris pv. campestris race 1.