Juvenile Resistance of Barley Cultivars and Accessions to Net-, Spot-, and Hybrid (Net × Spot) Forms of <i>Pyrenophora teres</i>

Abstract

Barley net blotch is an economically important disease. The causative agent is an ascomycete, Pyrenophora teres, which exists in two forms: P. teres f. teres (Ptt) and P. teres f. maculata (Ptm), which differ in their symptoms on barley plants. These two forms are easily crossed in laboratory conditions with the formation of fertile offspring, however, it is extremely difficult to prove the hybrid nature of fungal isolates, sometimes found in natural populations of the pathogen and bearing signs of both forms. In 2020, we first identified Ptt × Ptm hybrids in natural populations of P. teres in Krasnodar Region in isolates collected in 2016. The aim of the studies was to compare the virulence of two Ptt isolates, two Ptm isolates of different origin and a hybrid isolate Ptt × Ptm to a wide set of barley genotypes from the VIR collection pre-selected for Ptt resistance, to determine variability of the virulence trait in the hybrid isolate and characterize resistance to both forms of the fungus and hybrid. Depending on the barley genotype, 3 types of disease symptoms were manifested upon inoculation with the Ptt × Ptm hybrid isolate: (1) similar to Ptt, (2) similar to Ptm, and (3) a mixed type. Apparently, the manifestation of symptoms after inoculation with the hybrid isolate depends on the barley genotype influencing the expression of certain pathogen effector genes. It was shown that in most cases Ptm isolates differ in virulence from Ptt isolates to the same barley genotypes, and the Ptt × Ptm hybrid isolate from both Ptt and Ptm. On average, the Ptt × Ptm hybrid isolate was less aggressive than the Ptt and Ptm isolates. A comparison of the types of responses of barley genotypes to all studied isolates of Ptt and Ptm revealed 8.8% of genotypes resistant to both forms of P. teres and 5.6% to Ptt, Ptm and the hybrid isolate Ptt × Ptm. The virulence of natural hybrid between two forms of P. teres Ptt × Ptm was studied for the first time. The barley genotypes resistant to the two forms of the net blotch are valuable source of resistance for barley breeding.