Effects of Temperature on Disease Severity in Plants of Subterranean Clover Infected Singly or in Mixed Infection withBean yellow mosaic virusandKabatiella caulivora

Abstract

Many epidemics involve plants infected with more than one pathogen, but few experiments address climate change scenarios that influence mixed infections. This study addresses the interactive effects of co-infection and temperature on disease development in plants of the annual pasture species subterranean clover (Trifolium subterraneum), which is widely sown in different world regions. Bean yellow mosaic virus (BYMV) and the fungus Kabatiella caulivora are two important pathogens causing considerable production losses in pastures containing this species. Both occur together in such pastures causing a severe necrotic disease when mixed infection occurs. Effects of temperature on symptom expression were investigated in subterranean clover plants infected singly or in mixed infection with these pathogens. Plants were maintained in controlled environment rooms at 18°C, 20°C or 22.5°C after sap inoculation with BYMV. K. caulivora conidia suspensions were inoculated to plants once systemic BYMV symptoms developed. Plants were assessed for three disease assessment parameters, dead petioles numbers, marginal leaflet necrosis and overall plant damage. In general, mixed infection caused most severe symptoms, K. caulivora least severe symptoms, and BYMV symptoms of intermediate severity. In single infections, effects of temperature on disease severity differed between pathogens: BYMV symptoms were most pronounced at 18°C, but K. caulivora induced more severe symptoms at 20°C and 22.5°C. In mixed infections, disease severity generally followed the pattern developed with BYMV alone as temperature increased. Also, synergistic increase in disease severity sometimes occurred at 18°C, but increases were only additive at 20°C and 22.5°C. These results reflected the greater BYMV multiplication detected in infected leaves at 18°C compared with 20°C or 22.5°C. Our findings indicate that in rainfed subterranean clover pastures, as global warming progresses disease severity from infection with BYMV and K. caulivora alone may decline or increase, respectively, and mixed infection with them may become less damaging.

Phytopathogenic fungus hosts a plant virus: A naturally occurring cross-kingdom viral infection

“…The efficiency of CMV acquisition and transmission by R. solani should be tested under field conditions, and extensive screening of R. solani strains for the CMV infection would reveal the actual prevalence of viruliferous fungus in the field. Compared with virus transmission by common soil-borne vectors, transmission of a plant virus by a phytopathogenic fungus may pose a greater threat in the sense that simultaneous infection of two different pathogens could elicit more serious damage to the plant (59). Interestingly, our experiment showed synergistic effects of CMV infection on R. solani virulence in potato and N. benthamiana plants (Figs.…”

Long‐term viability of the northern anthracnose pathogen, Kabatiella caulivora, facilitates its transportation and spread

“…Many of the varieties of subterranean clover with resistance against K. caulivora race 1 are very susceptible to race 2 (Barbetti, , ; Bayliss et al ., ), and the threat of spread of race 2 more widely across southern Australia threatens more than 1 million hectares of varieties that currently have effective resistance against race 1 (M. J. Barbetti, unpublished data). Furthermore, the increasingly variable and changing climatic conditions will probably encourage development of further new races of K. caulivora (Guerret et al ., ), as is already happening with other fungal pathogens in Western Australia, such as Sclerotinia sclerotiorum on oilseed rape (Uloth et al ., ). Any such K. caulivora isolates that were better adapted to warmer conditions would pose a potential threat not only to currently affected regions, but also to regions where the disease is presently unimportant due to current unfavourable environmental conditions.…”

“…() highlighted a strong relationship between environment and disease development in subterranean clover forages, with mean temperatures of 11–17 °C and frequent rainfall favouring disease development. In contrast, others have reported that more severe disease symptoms occur at temperatures between 20 °C and 22.5 °C (Guerret et al ., ) or at temperatures between 20 °C and 24 °C (Cole & Couch, ; Darunday & Hanson, ). Prolonged warm to hot sunny weather stops disease development (Anderson et al ., ) and K. caulivora is inactivated when the temperature reaches 28 °C (Berkenkamp, ; Johnsson, ).…”

Influence of Abiotic and Biotic Factors on Productivity of Transgenic Soybean and Molecular Properties of Disease Pathogen

“…the introduction of new crop species and plant genotypes, and changes in husbandry practice (Roos al., 2011). It was shown that factors like CO 2 , elevated temperature and rainfallrelated parameters influence on plant viruses, eg, CMV,PVY, PVX (Del Torro et al, 2015) TYLCV, and TuMV (Chung et al, 2015), Potato leaf roll virus and Potato yellow vein virus (Jones, 2014), BYDV (Nancarrow et al, 2014;Rua et al, 2013), BYMV (Guerret et al, 2016), and several important their vectors (Gillespie et al, 2012). Increased soil moisture and temperature in temperate regions, including northern Europe, are expected to increase the activities of zoospores and nematodes that transmit viruses (Jones 2014;Roos al., 2011).…”