Effects of frequency of "extreme" temperature highs on development of soybean rust

Engineering Multigenerational Host-Modulated Microbiota against Soilborne Pathogens in Response to Global Climate Change

Crop migration caused by climatic events has favored the emergence of new soilborne diseases, resulting in the colonization of new niches (emerging infectious diseases, EIDs). Soilborne pathogens are extremely persistent in the environment. This is in large part due to their ability to reside in the soil for a long time, even without a host plant, using survival several strategies. In this regard, disease-suppressive soils, characterized by a low disease incidence due to the presence of antagonist microorganisms, can be an excellent opportunity for the study mechanisms of soil-induced immunity, which can be applied in the development of a new generation of bioinoculants. Therefore, here we review the main effects of climate change on crops and pathogens, as well as the potential use of soil-suppressive microbiota as a natural source of biocontrol agents. Based on results of previous studies, we also propose a strategy for the optimization of microbiota assemblages, selected using a host-mediated approach. This process involves an increase in and prevalence of specific taxa during the transition from a conducive to a suppressive soil. This strategy could be used as a model to engineer microbiota assemblages for pathogen suppression, as well as for the reduction of abiotic stresses created due to global climate change.

Distribution and Characteristics of Colletotrichum spp. Associated with Anthracnose of Strawberry in Hubei, China

Anthracnose caused by Colletotrichum spp. is a serious disease of strawberry. The etiology of anthracnose of strawberry is complex, and several Colletotrichum spp. have been regarded as causal agents. In the present study, multilocus (actin, β-tubulin, calmodulin, glyceraldehyde-3-phosphate dehydrogenase, and chitin synthase) phylogenetic analysis revealed that 100 isolates of Colletotrichum associated with anthracnose of strawberry in central China belong to five species. In total, 97 isolates were identified belonging to the Colletotrichum gloeosporioides species complex, with C. murrayae, C. gloeosporioides, C. fructicola, and C. aenigma accounting for 81, 8, 4, and 4% of the total isolates, respectively. Three isolates belonging to the C. acutatum complex were identified as C. nymphaeae. On inoculated strawberry plants, isolates of C. fructicola and C. murrayae species showed strong pathogenicity to both leaves and petioles of strawberry, with plant mortality 30 days after inoculation of 77.8 and 55.6%, respectively. C. gloeosporioides, C. aenigma, and C. nymphaeae showed strong pathogenicity to leaves but weak pathogenicity to petioles, with plant mortality 30 days after inoculation of 5.6, 16.7, and 11.1%, respectively. The five species were divided into four classes based on their maximum growth temperatures. Isolates of C. murrayae and C. gloeosporioides were more tolerant to high temperature (>34°C) than isolates of other species, followed by C. fructicola and C. aenigma. Isolates of C. nymphaeae, which are only distributed in areas of higher altitude (1,100 m), were highly sensitive to higher temperature. These results indicate that pathogenicity and adaptation to temperature are important factors in the distribution of Colletotrichum spp. on strawberry plants. This research may increase our understanding of how Colletotrichum spp. emerge and spread to geographical regions with different latitudes or elevations.

Morphology of Puccinia horiana, Causal Agent of Chrysanthemum White Rust, Sampled From Naturally Infected Plants

Chrysanthemum white rust (CWR), caused by Puccinia horiana, is pathogenic on many Chrysanthemum spp. and close relatives, and infects commercially important florist chrysanthemum cultivars (Chrysanthemum × morifolium) throughout the world. Due to regulations, most research and observations with CWR are done in vitro with symptomatic plants. In contrast, research presented herein is based on microscopic examination of symptomatic and asymptomatic plants collected from natural outbreaks in the field. We observed scattered (not in a linear pattern) telial sori on infected chrysanthemum leaves, stems, and flowers that coalesced at high infection levels. Teliospores were mainly two-celled but occasionally one- or three-celled. Promycelia arose from the apical teliospore cell, the basal cell, or both. The number of basidiospores on promycelia varied from one to four. Germ tubes, arising from P. horiana basidiospores, penetrated the host epidermis directly without appressoria. A mucilaginous exudate formed at the site of attachment and penetration of leaf and stem tissue, as well as on internal cell walls. P. horiana colonization was systemic, with intercellular mycelium and intracellular M-haustoria in both symptomatic and asymptomatic infected host tissue. Hyphal anastomosis was observed within infected plants, suggesting that asexual fusion between different P. horiana pathotypes or genotypes might occur.