Identification of two novel pathovars of Pantoea stewartii subsp. indologenes affecting Allium sp. and millets

Pantoea stewartii subsp. indologenes is a causative agent of leafspot of foxtail millet and pearl millet; however, novel strains were recently identified that are pathogenic on onion. We phenotypically and genotypically characterized seventeen Pantoea stewartii subsp. indologenes strains from onion and other sources (pearl millet, foxtail millet, guar pulse, verbena and corn). Based on the host range evaluation, we propose two pathovars P. stewartii subsp. indologenes pv. cepacicola pv. nov. and P. stewartii subsp. indologenes pv. setariae pv. nov. Pantoea stewartii subsp. indologenes pv. cepacicola pv. nov. causes symptoms on Allium species (leek, onion, chive and Japanese bunching onion) and also on foxtail millet, pearl millet and oat. However, P. stewartii subsp. indologenes pv. setariae pv. nov can only infect the members of Poaceae (foxtail millet, pearl millet and oat). Our study also showed that P. stewartii subsp. indologenes pathovars and P. stewartii subsp. stewartii share high genotypic relatedness and cannot be differentiated by dDDH and ANI values. Although, the newly proposed pathovars are not clearly distinguishable by their fatty acid and methyl esterase profiles, and substrate utilization patterns, a fatty acid (unknown with retention time: 10.9525) and few metabolites (3 methyl glucose, Na butyrate and fusidic acid) can be potentially used to distinguish them. We also report the distribution of previously known pathogenicity (HiVir, hrcC) and virulence (alt) factors of Pantoea sp. in the new pathovars. The impact of these new pathovars in the center rot pathosystem of onion is yet to be determined.

Yielding and nutritional value of Japanese bunching onion in relation to the date of planting and type of flat cover

ABSTRACT During a three-year field experiment, the possibilities of cultivating the ‘Performer’ cultivar of Japanese bunching onion for early harvest bunching were assessed through the use of autumn and spring planting terms. The seedlings, produced in multi-pots, were planted in the open field on 8-10 September, 9-10 October and 6-12 April, and covered with a perforated foil and agrotextile in mid-November or directly following the spring planting. The covers were removed at the end of April, and the harvest of Japanese bunching onion was conducted at the end of May. The percentage of plants that survived the winter, how many produced flowering stems and the height of the total and marketable yield of plants with a pseudostem diameter >10 mm were determined. We evaluated the content of selected components with a nutritional value in samples of edible plant parts. The results of the study showed that it is possible to obtain a high yield of plants harvested for bunches following an early spring term seedling planting. The majority of plants planted in the autumn froze during the winter, while those that were overwintered produced flower stems, especially if planted in September. The application of flat covers increased the percentage of plants that survived the winter, though in spite of this fact, the obtained marketable yield of Japanese bunching onion planted in the autumn was very low. Plants from the spring planting were characterised by a lower content of dry matter, chlorophyll a+b and volatile oils, while their content of K, Ca and Mg showed enhanced levels. Covering plants with a perforated foil positively influenced the content of total sugars and volatile oils, while negatively influencing the amounts of vitamin C, potassium and calcium as compared to those cultivated without covers.