Reaction and survival of four types of sunflowers against Sclerotinia sclerotiorum under controlled conditions

摘要

Sclerotinia wilt of sunflower caused by Sclerotinia sclerotiorum (Lib.) De Bary is the major disease of sunflower (Helianthus annuus L.) in Iran. North-western areas of Iran demonstrate the most yield losses through the disease. Development of cultivars with adequate genetic resistance is necessary to avoid these losses. Evaluation of sunflower genotypes varies based on researchers and environmental conditions. Meanwhile, greenhouse tests of the sunflower genotypes are more reliable because of controlled conditions during the assessment activities. To study the reaction of the host plants under controlled conditions, three stem inoculation techniques, including mycelium plug (MP), oxalic acid solution (OAS) and wheat seeds infested (IWS) with Sclerotinia mycelium, were employed. Wounded and non-wounded treatments were used in the experiment to find their effect on the disease progress. Four genotypes, including Ghalami (local variety in market), Confeta, Alstar and Master, were inoculated in this study. The factor was the lesion length to evaluate the effectiveness of different inoculation procedures. The lesion length was measured after 3, 7, 10 and 14 days post inoculation. The analysis of variance demonstrated significant differences between IWS and two other methods (MP and OAS), where the IWS produced the longest lesion lengths. In contrast, the non-significant differences between MP and OAS methods might help researchers to employ the pathogenicity factor (oxalic acid) as an alternative inoculum for their studies. Master variety was the most tolerant genotype among the treatments and its viability was 100% even at 14days after inoculation and incubation. Interestingly, there was no mortality in all cultivars before 7-day incubations, regardless of resistant or susceptible reactions.