Carbon source dependent-anaerobic soil disinfestation (ASD) mitigates the sclerotial germination of Sclerotinia sclerotiorum

Abstract

Though Sclerotinia sclerotiorum is a well-studied plant pathogen that causes significant economic damage worldwide, sustainable and environmental friendly control methods are difficult to establish due to it wide host range, cosmopolitan distribution and production of recalcitrant structures that can survive in soil for a long time. The pathogen was found causing a severe disease incidence on cabbage in 2016 in Sri Lanka. It was hypothesized that a) isolates of the recent disease outbreak display cross resistance to commonly applied fungicides and b) carbon (C) source supplemented Anaerobic Soil Disinfestation (ASD) is effective in mitigating the germination of sclerotia. In vitro fungicide sensitivity assays showed large variation in mycelial growth inhibition indicating high adaptability of the population towards environmental fluctuations and management practices. Signatures of cross resistance were evident. ASD was carried out using cabbage (Brassica oleracea) and leek (Allium ampeloprasum) cull piles, durian (Durio zibethinus) peels and grass cuttings (Axonopus compressus) as C sources and determined the sclerotial viability. Cabbage and leek cull piles at rates of 60-100 mg/g soil completely inhibited sclerotial germination. Maintaining anaerobic condition along with C source amendments was found to be a critical step in mitigating the sclerotial germination. GC-MS analysis of the volatiles of cabbage leaves, leeks and durian further confirmed the presence of various bioactive compounds with potential antifungal activity. Therefore, in addition to elevated microbial activity in treatments, the volatiles of C sources may have helped mitigating sclerotial germination.

Genetic Diversity and Recombination in the Plant Pathogen Sclerotinia sclerotiorum Detected in Sri Lanka

“…However, genotypic diversity was relatively lower than that of the Attanayake et al [30]. The average gene diversity of microsatellite loci (H¬e = 0.56) was analogous to those reported for non-clonal populations (He = 0.40-0.71) of S. sclerotiorum [6,35]. We observed a higher haplotype frequency (49%) than what is reported for clonal pathogen populations in the USA [36] and recombining populations in the North Central United States [34].…”

“…No complete resistant cultivars are available for many host crops including cabbage [2] and fungicide application is a widely used management practice. High levels of variation in fungicide insensitivities among S. sclerotiorum isolates have been reported in the USA [3], China [4], Iran [5], Sri Lanka [6], and other European countries [7]. However, the selected fungicide should be effective against all the genotypes and most importantly, the prevalent genotype of a population to achieve the best disease management.…”

“…In Sri Lanka, S. sclerotiorum on cabbage (Brassica oleracea L.) was first reported in 2014 [18] and since then, the disease has been detected in commercial cabbage fields from time to time. However, except only two studies on pathogen phenotypic diversity [19] and anaerobic soil disinfestation based disease management [6], no population genetics studies of S. sclerotiorum have been conducted in Sri Lanka. Hence, Sri Lanka provides an excellent location to study the genetic diversity and population structure of S. sclerotiorum under tropical climate.…”

Can Anaerobic Soil Disinfestation (ASD) be a Game Changer in Tropical Agriculture?

“…Similarly, the application of rice bran-treated soils emitted a spectrum of volatile compounds containing organic acids, alcohols, and esters [ 50 , 66 ]. Mahalingam et al [ 55 ] conducting a gas chromatography-mass spectrometry (GC-MS) analysis of cabbage and leek cull piles reported the presence of antifungal volatiles.…”

“…This method was first described independently by researchers in Japan [ 42 , 43 ] and in the Netherlands [ 44 ] and was later adapted to the USA [ 45 ] to control soil-borne pathogens in strawberry and vegetable fields. Thereafter, researchers around the world started applying this method, showing a great potential to control various soil-borne phytopathogens [ 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ].…”