Biology of pyrenophora spot blotch on barley (Hordeum vulgare L.) incited by Pyrenophora teres Drechs. F. Sp. Maculata Smedeg. and genetics of resistance
Karki, Chandra Bahadur
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Pyrenophora spot blotch (PSB) caused by Pyrenophora teres Drechs. f. sp. macu/ata Smedeg. is a newly reported and an important disease on barley (Hordeum vu/gare L.) in Montana and other parts of the world. Research was initiated to gain a better understanding of the disease, pathogen and host parasite interaction. Tests conducted to determine the pathogenic variation of 14 PSB isolates from Montana, Morocco, Tunisia, and Turkey using 20 barley cuItivars under growth chamber conditions showed smaller lesions and higher amount of chlorosis and necrosis with the Montana isolates than with isolates from North Africa and Turkey. Cultivars Unitan, Cl 9214, Cl 5401, Cl 9440 and Cl 9776 were resistant and Dekap, KIages, Nupana and Cl 13727 were susceptible to all isolates. Cultivars Cl 7584, Cl 9819, Cl 9825 and Tifang showed differential reactions between the PSB isolates from Montana and other countries. Isolates Turk 74-Pt6, Tun 79-30, Mts Plent82 and Mts Eddy 82-5 were the most virulent among 15 isolates. A study on conidium and conidio-phore characteristics of PSB isolates revealed that isolates from Morocco and Tunisia produced significantly longer conidiophores while Montana isolates produced a higher number of geniculations. The basal conidium cell was rounded in Montana isolates and conical or snake-headed in the isolates from North Africa. A comparison of two isolates from Montana and Morocco showed no differential effects on yield components and spike length averaged over four barley cultivars. Infected cuItivar Dekap showed reductions as high as 75% in kernel number and 16% in kernel weight. Symptoms varied between cultivars screened in the growth chamber and in the field. Cultivars Tifang, Minn 21, Himalaya, Oderbrucker, Cl 1615, Cl 5401, Cl 6475, Cl 9214, Cl, 9440 and Cl 9776 were resistant in both conditions. Cultivars showing good sources of resistance were studied in the F1 F2 and BC1 generations to determine gene action and gene number conditioning resistance to a PSB isolate. Crosses involving resistant and susceptible barley cultivars showed often a monogenic or digenic recessive resistance in the growth chamber and often a monogenic or digenic dominant resistance in the field. Among the various crosses evidence was also found for multigenic resistance, maternal inheritance, transgressive segregation, and no allelism.