Use of different methods for the control of pink root rot disease (Pyrenochaeta terrestris) 'Hansen' of onion (Allium cepa L.) in Nyala province

The results of this study proved that the prevalence of pink root rot disease of onion (Allium cepa L.) caused by the fungus Pyrenchaeta terrestris (Hansen). Gorenz. Walker and Larson. Was extremely high, to the extent that some onion producers gave up onion production and shifted to other vegetables: 100prevalence in kass locality, followed by 95in Bilel locality and the lowest was 45in Mershing locality. Three isolates of the disease causal fungus were established in pure cultures namely Bilel isolate. Mershing isolate and kass isolate. It was also found that the temperature range of 25 to 27**C was optimum for the fungus growth on PDA medium in the laboratory. The three isolates were successfully established in liquid medium composed of water and dextrose. The study also proved that the three isolates of pathogen Pyrenchaeta terrestris (Hansen) were pathognic to onion compared tonon-inoculated control. The invitro test of chemical fungicides for the control of Pyrenchaeta terrestris assuredthat the three chemicals were capable of controlling the fungus. However. Benlate (Benomyl) fungicide appeared to be the most effective followed by Captan. Thiram and thenZineb fungicides. The onion variety screening experiment confirmed that some Sudanese onion varieties expressed excellent resistance to pink rot disease. Varieties Furawia and Flatia were proved to be of good resistance during the first season of this experiment and produced more dry bulbs compared to the others. It was also found that the loss in dry bulb yield in the first season was very high to the extent that the percentages of the loss when comparing the yield of onion in infested soil compared to non-infested soil was almost approaching 100while in the second season of the experiment the yield loss was about 70. So from the two seasons we had 6 onion varieties which proved of excellent resistance, namely, Furawia, Flatia, Zalingi, Saggai improved. Hudeiba red improved and Nasi yellow. Variety Furawia showed 0disease index followed by Flatia 8.3varieties Zalingi and Saggal improved 33.3each, while the disease index for the varieties Hudeiba red improved and Nasi yellow were 41.7 and 45.8. repectively. The results of the effect of irrigation frequency on the incidence of pink root rot disease of onion (Pyrenchaeta terrestris) as reflected on the growth parameters and yield parameters of the tested oion revealed that the lowest disease index was recorded at the irrigation interval of 9 days during the first season of the experiment (54.5) compared to index of 62.3. 70.9and 71at intervals of 7 days. 5 days and 3 days respectively. Statistically no significant differences were observed among the 4 tested irrigation intervals on the growth and yield parameters for the tested onions during the two seasons. On the other hand, the results of the field chemical control experiment indicated that the lowest disease index was recorded on the onion plants treated with Benlate (Benomyl) (27.8) followed by Thiram and Zineb fungicides (33.3each) and then Captan (44.4) compared to untreated control (50). However, the difference was not statistically significant. The effect of the chemical control experiment using the above-mentioned fungicides as reflected on the growth and bulb yield parameters for the tested onion plants was not significant in spite of the fact that in the field the chemically treated onion plants appeared more healthy than the untreated control.