Effects of varieties and levels of cyanide content in cassava on mealybug populations

Abstract

The comparison of the levels of cyanogenic glycoside in cassava varieties and the effects on mealybug infested cassavas and increasing rate of mealybug population was conducted in a greenhouse using a Completely Randomized Design (CRD) with 4 treatments of cassava varieties: Kasetsart 50, Huaybong 80, Huaybong 60, and Rayong 72. The results showed no complete resistance of cassava varieties to mealybugs. Partial resistance was observed in different cassava varieties. Intrinsic rate of natural increase (r) of mealybugs in cassava varieties and carrying capacity (K) were positively related to the level of cyanide. Therefore, cyanogenic glucoside might be involved as mealybug attractant, not repellent; and it is not a factor in plant resistance to insects. The relationship between cyanogenic glycoside and number of mealybugsin 4 varieties of cassavas (Kasetsart 50, Huaybong 80, Huaybong 60 and Rayong 72) planted in different soils was studied by using Randomized Complete Block Design (RCBD) in 4 soil types in mealybug outbreak areas in Chaiyaphum and Khon Kaen provinces. Mealybug populations were determined for each of the 25 cassava varieties once a month for 8-10 months. The results found that cassavas in different areas had different levels of cyanogenic glycoside. The level of cyanogenic glycoside was highest in cassavas from Khon Kaen University. The results may have involved minerals in soils, and seasonal and cultural practices. The mealybug infestation in Rayong 72 variety was higher than that of other varieties. After harvesting, the results showed that Huaybong 80 variety provided the highest yield when compared to that of others.