Isolate-Dependent Inheritance of Resistance Against Pseudoperonospora cubensis in Cucumber

Abstract

Six wild accessions of Cucumis sativum were evaluated for resistance against each of the 23 isolates of the downy mildew oomycete Pseudoperonospora cubensis. The isolates originated from Israel, Europe, USA, and Asia. C. sativum PI 197088 (India) and PI 330628 (Pakistan) exhibited the highest level of resistance against multiple isolates of P. cubensis. Resistance was manifested as reduced lesion number, lesion size, sporangiophores and sporangia per lesion and enhanced encasement of haustoria with callose and intensive accumulation of lignin in lesions of both Plant Introductions (PIs) compared to the susceptible C. sativum SMR-18. In the field, much smaller AUDPC (Area Under Disease Progress Curve) values were recorded in PI 197088 or PI 330628 as compared to SMR-18. Each PI was crossed with SMR-18 and offspring progeny plants were exposed to inoculation with each of several isolates of P. cubensis in growth chambers and the field during six growing seasons. F1 plants showed partial resistance. F2 plants showed multiple phenotypes ranging from highly susceptible (S) to highly resistant (R, no symptoms) including moderately resistant (MR) phenotypes. The segregation ratio between phenotypes in growth chambers ranged from 3:1 to 1:15, depending on the isolate used for inoculation, suggesting that the number of genes, dominant, partially dominant, or recessive are responsible for resistance. In the field, the segregation ratio of 1:15, 1:14:1, or 1:9:6 was observed. F2 progeny plants of the cross between the two resistant PI’s were resistant, except for a few plants that were partially susceptible, suggesting that some of the resistance genes in PI 197088 and PI 330328 are not allelic.

Identification of Novel Loci and Candidate Genes for Cucumber Downy Mildew Resistance Using GWAS

“…Thus, we conclude that the CG germplasm is rich in DM resistance and offers valuable donors for breeding cucumber with resistance to DM. However, it is worthwhile to note that of the prevailing DM isolates, many change from one season to the other, and the DM resistance found in the CG lines might be race-specific [ 34 ]. This could be one of the explanations for why DI data of 2016 did not have good correlations with the other three experiments.…”

Effects of Nutrient Solution Irrigation Quantity and Downy Mildew Infection on Growth and Physiological Traits of Greenhouse Cucumber

“…Cucumber, as an important economic crop, is one of the main vegetables widely planted in the world. It has a status second only to tomato in fruit vegetables [8,9]. Because of its rich taste and nutritional value, cucumber is deeply loved by consumers and plays an increasingly important role in agricultural structure adjustment and farmers' income increase.…”

Classical Genetics and Traditional Breeding in Cucumber (Cucumis sativusL.)

“…Understanding the inheritance of downy mildew is fundamental to successful cucumber breeding programs. Downy mildew resistance is controlled by a single recessive gene [68,69], pair of dominant and recessive interacting genes [70], two recessive genes in PI 197088 and a single recessive gene in 'Poinsett' [71], three recessive genes, dm-1, dm-2 and dm-3 [72], two incompletely dominant genes [73], inheritance for downey mildew resistance is quantitative [24][25][26]74], number of genes, dominant, partially dominant, or recessive are responsible for resistance [75], multiple recessive genes [76]. The cucumber accession PI 197087 from India and its derivatives like Gy14 are resistant to downy mildew that is conferred by dm-1.…”