Comparative Transcriptome Analyses Reveal Conserved and Distinct Mechanisms of the SDHI Fungicide Benzovindiflupyr Inhibiting Colletotrichum

Colletotrichum leaf disease (CLD) is an annual production concern for commercial growers worldwide. The succinate dehydrogenase inhibitor (SDHI) fungicide benzovindiflupyr shows higher bioactivity against CLD than other SDHIs. However, the mechanism underlying such difference remains unclear. In this study, benzovindiflupyr exhibit good inhibitory activity against C. siamense and C. nymphaeae in vitro and in vivo. To reveal its mechanism for inhibiting Colletotrichum, we compared transcriptomes of C. siamense and C. nymphaeae under treatment with benzovindiflupyr and boscalid. Benzovindiflupyr exhibited higher inhibitory activity against SDH enzyme than boscalid, resulting in a greater reduction in the ATP content of Colletotrichum isolates. Most of the metabolic pathways induced in these fungicide-treated isolates were similar, indicating that benzovindiflupyr exhibited a conserved mechanism of SDHIs inhibiting Colletotrichum. At the same level of suppressive SDH activity, benzovindiflupyr activated more than three times greater gene numbers of Colletotrichum than boscalid, suggesting that benzovindiflupyr could activate distinct mechanisms against Colletotrichum. Especially, membrane-related gene ontology terms, mainly including intrinsic components of membrane, were highly abundant for the benzovindiflupyr-treated isolates rather than boscalid-treated isolates. Only benzovindiflupyr increased the relative conductivities of hyphae, indicating that it could damage the cell membrane and increase of mycelial electrolyte leakage. Thus, we proposed that the high bioactivity of benzovindiflupyr against Colletotrichum by inhibiting SDH activity and damaging the cell membrane at the same time. The research improves our understanding the mode of action of SDHI fungicides against Colletotrichum.

Distribution and Fungicide Sensitivity of Colletotrichum Species Complexes from Rubber Tree in Hainan, China

Colletotrichum gloeosporioides and C. acutatum species complexes are causal agents of Colletotrichum leaf disease (CLD) of rubber trees worldwide. To determine the geographic distribution of Colletotrichum species complexes associated with CLD of rubber trees in Hainan, China, and their sensitivity to fungicides used in the region, a total of 275 Colletotrichum isolates were collected from 52 rubber tree plantations in 11 counties. These isolates were identified based jointly on morphological characteristics and PCR-based methodology. Of these isolates, 78 and 22% belonged to the C. gloeosporioides species complex (CGSC) and the C. acutatum complex (CASC), respectively. The incidence of CGSC isolates was greater than the CASC in all counties sampled. The incidence of CASC isolates appeared to be lower in the western and central south of Hainan than in other regions. There was no association in their presence at a given plantation between the two species complexes. The in vitro sensitivity of these two species complexes to carbendazim, chlorothalonil, and four demethylation inhibitor (DMI) fungicides (difenoconazole, propiconazole, myclobutanil, and prochloraz) was determined. Carbendazim was effective against CGSC but not against CASC with mean ED50 values of 0.176 and 2.182 µg/ml, respectively. CASC isolates were more sensitive to difenoconazole, propiconazole, and myclobutanil (mean ED50 values of 0.177, 0.129, and 1.424 µg/ml, respectively) than CGSC isolates (mean ED50 values of 0.710, 0.348, and 3.496 µg/ml, respectively). Mean ED50 values of CGSC against chlorothalonil and prochloraz were 173.341 and 0.035 µg/ml, respectively; corresponding values for CASC were 151.441 and 0.040 µg/ml. These results suggest that prochloraz, propiconazole, and difenoconazole are effective against both species complexes.