Inheritance of resistance to downy mildew by F1 and F2 sunflower hybrids

Abstract

Downy mildew belongs to the 40 most common sunflower diseases in the world (which are registered as the main ones), is found on crops all over the world, and is the most harmful among them, since this pathogen can affect 100% of plants under favorable for development conditions. Identification of a dominant race of this pathogen in the Eastern Forest-Steppe ofUkraineand determination of an inheritance type for sunflower hybrid breeding make our study topical.

The aim and tasks of the study. Our objective was to determine the genetic control of resistance to downy mildew in F₁ and F₂ sunflower hybrids.

Materials and methods. Incidence of downy mildew on sunflower accessions was evaluated in an infectious site of the Laboratory of Plant Immunity against Diseases and Pests of the Plant Production Institute of nd a VYa Yuryev of NAAS. Provocative background was created by reduced crop rotation of (four-field crop rotation). The predecessor was millet. The agricultural technology was conventional for the Forest-Steppe of Ukraine. Resistance of sunflower accessions was determined by the disease incidence. Pl. helianthi was detected by assessing affection of lines-differentators. To determine donor properties of previously developed parents, female lines and lines - sunflower pollen fertility restorers, and to determine the inheritance type of resistance to this pathogen, hybridologic analysis of 25 F₁ and F₂ hybrid combinations obtained from test crosses in 2014 was performed. The degree of phenotypic dominance (hp) in F₁ hybrids was determined, and congruity between the observed segregation and the hypothetical one in F₂ hybrids was assessed by χ².

Results and discussion. Analysis of the degree of dominance of resistance to downy mildew in F₁ hybrids demonstrated all types of inheritance, except for negative overdominance. In F₂ hybrid population, monogenic control of resistance was detected from crosses both with stable and with susceptible parents. Segregation of F₂ plants to resistant and susceptible ones (3:1) revealed one dominant resistance gene in hybrid combinations SKh1 A / BI 27 V, SKh1 A / BI 51 V, SKh3 A / BI 7 V (203/2, 203/3), SKh1 A / BI 10 V, SKh3 A / BI 37 V.

More than half (57.1%) of F₂ hybrids from crosses with resistant parents showed the segregation of 9:7, indicating two complementary dominant genes controlling resistance. This type of segregation was observed in hybrid combinations SKh 1 A / BI 27 V, SKh 1 A / BI 51 V, SKh 1 A / BI 198 V and SKh 3 A / BI 198 SKh. In F₂ hybrid combination SKh3 A / BI 26 V, the segregation of phenotypes was 37:27, indicating trihybrid segregation and control of disease resistance by three recessive genes with duplicate interaction. The segregation of phenotypes in F₂ hybrids generated from susceptible to pathogen male lines revealed monogenic segregation (3:1) in hybrid combinations SKh 3 A / BI 7 v, SKh 1 A / BI 10 V, SKh 3 A / BI 37 V. Dihybrid segregation (9:7) suggests the presence of two complementary dominant resistance genes in hybrids combinations SKh 5 A / BI 7 V, SKh 1 A / BI 39 V. Two duplicate dominant resistance factors were found by congruity to the theoretically expected phenotypic ratio of 15:1 in F₂ hybrids in combinations of SKh3 A / BI 7 V. Trihybrid segregation and control of resistance to disease by one dominant and two recessive genes, with duplicate interaction between, were detected by the ratio of resistant phenotypes to susceptible ones of 55:9 in hybrid combinations SKh 3A / BI 7 V, SKh1 A / BI 39 V from susceptible male lines.

Thus, the long-term selection of genotypes for resistance to race 730 of downy mildew pathogen among lines and evaluation on the epiphytotinous level of pathogen with race 732 occurring found that 2 resistant parents, BI 27 V and BI 51 V, produced hybrid families both with one dominant gene and with two complementary genes of resistance. Resistant pollen fertility restorer BI 198 V manifested itself in the offspring by two dominant complementary genes of resistance to the disease.

Parents BI 10V and BI 37V, which were susceptible to race 732 of downy mildew pathogen, as the assessment in 2016 showed, had one dominant gene according to resistance expression in F₂ hybrids. Two dominant resistance genes in F₂ hybrids are provided by line BI 7V, with complementary (9:7) and duplicate (15:1) interactions between them. As judged by the ratios of phenotypes of 9:7 and 55:9 in F₂ hybrids, susceptible sunflower pollen fertility restorer BI 39 V showed the presence both of two dominant complementary resistance genes and of one dominant and two recessive genes with duplicate interaction.

Conclusions. Hybridological analysis of F₁ and F₂ sunflower hybrids determined the nature of genetic control of resistance to downy mildew. In F₂ hybrid population, monogenic, digenic and trigenic control of resistance to this pathogen was observed in hybrids obtained from crosses both with resistant and with susceptible parents.

We compared the observed segregation into resistant and susceptible to downy mildew phenotypes in F₂ hybrid population with the theoretically expected monogenic control, and the real extended range of interactions between dominant, dominant complementary and dominant duplicate genes of resistance as well as between dominant and two recessive genes can be attributed to the influence of race 732 that is more virulent than race 730, and in previous years lines had been bred for resistance to race 730. However, the results of hybridologic analysis give grounds to recommend using lines - pollen fertility restorers BI 7 V, BI 27 V, BI 51 V, and BI 198 V as valuable starting material having dominant factors of resistance to downy mildew in breeding programs