<i>Albugo candida</i> race diversity, ploidy and host-associated microbes revealed using DNA sequence capture on diseased plants in the field

• Physiological races of the oomycete Albugo candida are biotrophic pathogens of diverse plant species, primarily the Brassicaceae, and cause infections that suppress host immunity to other pathogens. However, A. candida race diversity and the consequences of host immunosuppression are poorly understood in the field. • We report a method that enables sequencing of DNA of plant pathogens and plant-associated microbes directly from field samples (Pathogen Enrichment Sequencing: PenSeq). We apply this method to explore race diversity in A. candida and to detect A. candida-associated microbes in the field (91 A. candida-infected plants).• We show with unprecedented resolution that each host plant species supports colonization by one of 17 distinct phylogenetic lineages, each with an unique repertoire of effector candidate alleles. These data reveal the crucial role of sexual and asexual reproduction, polyploidy and host domestication in A. candida specialization on distinct plant species. Our bait design also enabled phylogenetic assignment of DNA sequences from bacteria and fungi from plants in the field.• This paper shows that targeted sequencing has a great potential for the study of pathogen populations while they are colonizing their hosts. This method could be applied to other microbes, especially to those that cannot be cultured

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Not AvailableAlternaria blight of crucifers caused by Alternaria brassicae and A. brassicicola causes unavoidable economic losses. The disease progression under field conditions is mainly influenced by environmental conditions, including temperature range of 15-25C, relative humidity >90 per cent, wind velocity of 2-5 kmh with intermittent rains. Disease forecasting models have been developed taking into account the leaf wetness period, number of rainy days, minimum, maximum, and optimum temperatures, relative humidity, date of sowing, variety, and species of Brassica crops grown under different agro-ecological conditions. Management of any disease is difficult with a single method or approach, to make it feasible, viable, stable, effective, and economical measures need to be taken. It is crucial to integrate all possible methods of plant disease management including cultural, chemical, biological, and host plant resistance for effective management of Alternaria blight of Brassicaceous plants.Not Availabl

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Response of interspecific Brassica juncea/Brassica rapa hybrids and their advanced progenies to Albugo candida (white blister)

Transfer of factors for resistance to white blister disease caused by Albugo candida between Brassica species involving two genotypes each of B. juncea and B. rapa was studied in hybrids. More hybrids were obtained by in vivo than in vitro techniques, although an in vitro phase was a prerequisite for the establishment of in vivo hybrids. Hybrids were identified by PCR-based inter-simple sequence repeat (ISSR) markers with both male and female species-specific bands being identified. There was a positive correlation between disease severity and number of days after sowing (r > 0.93), the highest being towards pod formation and plant maturity at 110 days after sowing. The plants from F-2 and BC1 progeny showed higher resistance to A. candida than either of the parents. Plants of B. juncea and B. rapa with high field resistance (disease index < 1.0) were selected from BC2 and F2BC1 generations. The frequency of plants classified as resistant in BC2 progeny ranged from 4.5 to 39.0% in cross-combinations involving B. juncea genotypes as female parent, compared with 100% in the reciprocal cross involving B. rapa as female parent