engleski

Susceptibility of sunflower breeding material to Alternaria sp.

In Croatia the leaf and stem spot disease caused by Alternaria species is considered as a disease associated with senescent plants and of minor importance. During 2008, 2009 and 2010 year Alternaria sp. isolated in a higher percentage on all sunflower growing location in areas of Eastern Croatia. On some locations except leaf lesions, stem lesions occured more frequently, they coalesced and form large blackened areas, resulting in stem breakage. Management practice in order to control this disease include use less susceptible varieties and hybrids, rotate sunflowers and seed fungicides treatments. Since that Alternaria disease in recent years occured more frequently on stems the aim of our research was to compare pathogenicity of A. helianthi, Alternaria sp. and A. helianthinficiens to sunflower stem and estimate the tolerance of a eight sunflower lines to the Alternaria species. For artificial infection 5 isolates of Alternaria species were used. A. helianthi (isolate Alh1), Alternaria sp. (isolates Al4 and Al5) were isolated from naturally infected sunflower plants in Croatia (location Sopot). Two isolates of A. helianthinficiens (E.G.S. 36-184 and 50-174, CBS 208.86) courtesy of Emory G. Simmons. Longitudinal lesion length on stems were measured 10 and 20 days after inoculation. *Average lesion length on inoculated sunflower plants with isolate A. helianthi (Alh1) measured 10 days after inoculation were between 2.67cm and 3.25 cm. Other isolates caused significantly smaller lesions. Twenty day after inoculation lesion size on plants inoculated with isolate A. helianthi (Alh1) ranged from 4.01 to 4.87 cm. Lesions on plants inoculated with isolates Alternaria sp. and A. helianthinficiens were smaller and varied from 1.0 cm (isolate E.G.S. 36-184) to 2.07 cm (isolate E.G.S. 50-174). Statistical differences in susceptibility between tested sunflower lines were determined after artificial infection with all tested isolates. Observing the differences in pathogenicity between the isolates, regardless of sunflower lines and days after inoculation the most pathogenic was isolate A. helianthi. Mean stem lesion size caused by A. helianthi 10 and 20 days after inoculation were 3.01 and 4.07, respectively. Ten days after artificial infection with A. helianthi isolate variation in susceptibility of tested sunflower lines were not found, 20 days later on two lines (DP- 3 and DP-4) statistically smaller lesions were measured. The results of this work indicate that A. helianthi compared with other tested Alternaria sp. is the most pathogenic for artificialy infected sunflower stem. Other tested Alternaria species caused significantly shorter lesion. A. helianthi can cause leaf and stem lesions, seedling blight and head rot. It has been reported to reduce seed and oil yield up to 84% and 33%, respectively, photosynthetic reduction of around 20%, 1, 000-seed weight and number of seeds produced per head The most economical and effective means to control sunflower diseases and other pests is planting resistant or tolerant hybrids.

Alternaria ; sunflower ; tolerance

nije evidentirano