Potential of Fusarium sacchari-tolerant mutants in controlling Eldana saccharina and borer-associated Fusarium stem rot in sugarcane

Abstract

Some Fusarium spp. such as F. sacchari PNG40, found in association with the African sugarcane stalk borer Eldana saccharina, have potential in biological control against the insect. However, Fusarium can cause stem rot in sugarcane thereby constraining its application. The present study tested the usefulness of F. sacchari PNG40 tolerant sugarcane mutants in the control of Fusarium stem rot and E. saccharina using endophytic F. sacchari PNG40. In vitro mutagenesis and selection of embryogenic calli (cultivar N41) were employed to produce F. sacchari-tolerant mutants. Stalks of 8 months-old N41 mutants and previously-produced NCo376 mutants were inoculated with PNG40 and then with E. saccharina 2nd instar larvae after 3 weeks. Length bored was 36–82 % less in inoculated stalks (1.00–4.67 cm) of the NCo376 and N41 mutants and their respective parents than their uninoculated controls (3.83–8.67 cm). Mass gain was significantly less in larvae retrieved from incubated stalks (0.028–0.045 g) of MutA and MutE of NCo376, and Mut1 and Mut27 of N41 than their controls (0.054–0.072 g). The NCo376 and N41 mutants displayed significantly less percent stalk area discoloured (Fusarium stem rot) (10.6–22.0 %) than their respective parents (N41 - 28.9 % and NCo376 - 30.2 %). Re-isolation of PNG40 from undamaged tissue indicated endophytic colonisation. MutA of NCo376 and Mut1 and Mut23 of N41 were identified for future field studies aimed at curbing Fusarium stem rot and developing endophytic Fusarium-mediated biological control against E. saccharina, as part of an integrated pest management approach.