Inheritance of resistance against Peronospora destructor in onion cv. ‘Regia’

Onion downy mildew (DM) caused by Peronospora destructor is a very destructive leaf disease. Genetic resistance is an economic and environmentally friendly way of disease control. In this research, the segregation of DM resistance was analysed in six offspring from crosses between national cultivars and the cv. ‘Regia’, a partial resistance source. F1 plants were self-fertilised, and F1S1 derived progenies were evaluated. The segregations in DM severity were skewed towards susceptibility, with transgressive segregation in five of six progenies. The recessive inheritance could be associated with loss of susceptibility mechanisms. In another experiment, the response of advanced F1S2 lines ‘Regia’ x ‘Pantanoso del Sauce’ were evaluated two times (August and November 2017) in DM disease severity, DM histological quantitative differences, and agronomic traits. F1S2 lines, which have had an earlier selection process, presented an intermediate DM severity between the parents. Disease severity was positively correlated with histological differences in the proportion of infected stomata. ‘Regia’ presented the lowest DM severity and the highest percentage of healthy stomata. Most resistant F1S2 lines did not differ from control cultivars in bulb yield, bulb quality traits and postharvest behaviour, and could be the basis to develop a DM resistant cultivar in comparison to currently grown cultivars

Factors Influencing the Occurrence of Onion Downy Mildew (Peronospora destructor) Epidemics: Trends from 31 Years of Observational Data

Onion downy mildew (ODM) caused by Peronospora destructor has been increasing annually in south-western Québec since the early 2000s, reaching 33% of affected onion fields in 2014. Using observational data collected over a period of 31 consecutive years, this study aimed to investigate the variations in ODM incidence and epidemic onset and identify the meteorological variables that influence its polyetic development. A logistic model was fitted to each ODM epidemic to estimate and compare the onset of epidemics on a regional basis. Results of this analysis showed that the first observation date, 10% epidemic onset (b10) and mid-time (b) were, on average, 30.4, 15.1 and 11.3 days earlier in 2007–2017 than in 1987–1996. Results of a principal component analysis suggested that regional disease incidence was mostly influenced by the precipitation regime, the final regional disease incidence the previous year, and warmer temperature during the harvest period the previous fall. Subsequently, the data were divided in three periods of 10, 10 and 11 years, and a discriminant analysis was performed to classify each year in the correct period. Using a sufficient subset of five discriminating variables (temperature and rainfall at harvest the previous fall, winter coldness, solar radiation, and disease incidence the previous year), it was possible to classify 93.5% of the ODM epidemics in the period where they belong. These results suggest that P. destructor may overwinter under northern latitudes and help to highlight the need for more research on overwintering and for the development of molecular-based tools enabling the monitoring of initial and secondary inoculum.

Молекулярные маркеры в селекции лука репчатого

Исследования проведены в 2016–2018 годах в лаборатории генетики, селекции и биотехнологии овощных культур РГАУ-МСХА им. К.А. Тимирязева. Целью исследования являлась оценка эффективности известных молекулярных маркеров различных типов цитоплазмы CMS-S, CMS-T и N, гена закрепителя стерильности и восстановителя фертильности и гена, контролирующего устойчивость к пероноспорозу. Рекомендованные в научной литературе молекулярные маркеры orfA501 и 5» cob позволяют дифференцировать растения лука репчатого по трем типам цитоплазмы – CMS-S, CMS-T и N-цитоплазма. В нашем исследовании с использованием этих двух маркерных систем установлены типы цитоплазмы всех проанализированных растений с мужской стерильностью. У шести образцов выявлена CMS-S цитоплазма, у четырех образцов CMS-T и два образца обладали нормальной (N) цитоплазмой. Для создания линий закрепителей стерильности необходимо использование образцов с N-цитоплазмой, так как они должны обладать генотипом Nmsms. При классическом способе используют анализирующие скрещивания, где в качестве тестера берут стерильные растения с генотипом Smsms или Тmsms. И по потомству полученных F1 гибридов судят о генотипе опылителя. Это требует как минимум 4 года работы. C помощью маркера Jnurf 13 проводят генотипирование на аллельное состояние локуса закрепления стерильности (msms) у растений с N-цитоплазмой, что сокращает процесс создания закрепителей стерильности в 4 раза. Доказано, что полная устойчивость Allium roylei к пероноспорозу контролируется одним доминантным геном Pd1. Маркер DMR1 выявляет наличие гена устойчивости Pd1 к ложной мучнистой росе. ПЦР-анализ с маркером DMR1 показал, что у устойчивого гибрида F1 Santero ген устойчивости находится в гетерозиготном состоянии, у восприимчивых сортов Денсити и Кенди – в рецессивной гомозиготы. В потомствах растений Sx (SxДенс) и Sx (SxКенди) наблюдали расщепление на устойчивые и восприимчивые, а среди устойчивых выявлены гомо- и гетерозиготные по гену Pd1.The studies were conducted in 2016–2018 in the laboratory of genetics, breeding and biotechnology of vegetable crops of the RSAU – MTAA. The aim of the research is to assess the efficiency of known molecular markers orfA501 и 5» cob to genotype a type of onion (Allium cepa L.) male sterility inducing cytoplasm’s, CMS- (S) and CMS- (T) and normal (N) cytoplasm, to genotype restorer fertility and maintainer sterility alleles Ms/ms of a nuclear gene, marker of onion downy mildew resistance gene. The use of these two marker systems (orfA501 и 5» cob) confirmed the type of cytoplasm of all screened male sterility onion plants. Six onion accessions had CMS-S type of cytoplasm, four accessions – CMS-T and two accessions had normal N-cytoplasm. The efficiency of recommended DNA-marker JnurF13 to genotype restorer fertility (Ms) allele and maintainer sterility (ms) allele of a nuclear gene was confirmed using a set of different onion accessions. The use of molecular marker Jnurf 13 helps to genotype the onion plant in relation to allelic state of the sterility maintainer allele (ms) in plants with N-cytoplasm and shortens the process of developing sterility maintainer lines. Allium roylei is completely resistant to downy mildew which is controlled by a single dominant Pd1 gene. Marker DMR1 of onion downy mildew resistance gene was studied using an accessions of Timofeev’s plant breeding station (RSAU – MTAA) involved in a breeding programs and commercial cultivars of foreign companies.

An Epidemic of Downy Mildew caused by Peronospora destructor on Vidalia Sweet Onions in Georgia in 2012

The first reported occurrence of onion downy mildew (ODM) on Vidalia sweet onions in Georgia was in 1999. Although the disease is not common every year, two epidemics have occurred since 1999. The authors report here on the impact of a recent outbreak of ODM on the $100-million Vidalia onion crop in 2012. Accepted for publication 29 January 2013. Published 28 March 2013.