First report of Golovinomyces sp. causing powdery mildew infection on Dyschoriste nagchana in Western Ghats of India

Dyschoriste nagchana Nees (Acanthaceae) is a perennial plant grows naturally in wet grassland, but is now often also found in secondary bushland and grassland, including lawns. In January2019, severe powdery mildew symptoms were observed on the leaves and stem of D. nagchana (Fig.1, a). The infection was found to be very severe at that time on plant and because of severe infestation premature leaf fall was also observed. The occurrence of powdery mildew in its anamorphic form on D. nagchana. was first observed in the ranges of hills in Western Ghats pertaining to district Satara viz Yavateshwar (17°41’02.91”N 73°56’58.15”E and Elevation 3419ft) and Varoshi (17°52’04.42” N 73°45’03.12” E and Elevation 2834ft). later on, disease incidence was noticed from different areas of said district.

Phytohormonal and Transcriptomic Response of Hulless Barley Leaf in Response to Powdery Mildew Infection

Powdery mildew (PM) caused by Blumeria graminis (DC.) Golovin ex Speer f. sp. hordei Marchal (Bgh) is one of the major yield reducing diseases in hulless barley (Hordeum vulgare L. var. nudum Hook. f.). Genotypes with contrasting resistance to PM offer unique opportunities to explore the transcriptome in order to understand the expression changes in genes and pathways. In this study, we explored the phytohormone levels and transcriptome of a Bgh susceptible (XL19) and resistant (ZYM1288) hulless barley genotypes at 0, 5, 12, 24, and 36 h post infection (hpi) with Bgh. We found relatively higher levels of abscisic acid, jasmonic acid, salicylic acid, and cytokinins in ZYM1288. The transcriptome analyses identified 31,354 genes that were enriched in signaling, energy, and defense related pathways. Higher numbers of differentially expressed genes (DEGs) were found in XL19 as compared to ZYM1288 after 5 (3603 vs. 2341) and 12 hpi (3530 vs. 2416). However, after 24 and 36 hpi, the number of DEGs was higher in ZYM1288 as compared to XL19 i.e., 3625 vs. 3034 and 5855 vs. 2725, respectively. Changes in hormone levels drove downstream expression changes in plant-hormone signaling that helped ZYM1288 to perform better under Bgh infection. The expression of DEGs in MAPK-signaling and Toll-like receptor signaling pathways, glucosinolate biosynthesis, glutathione metabolism, brassinosteroid metabolism, and energy related pathways indicated their common roles in defense against PM. Key genes related to PM-resistance were upregulated in the resistant genotype. These genes provide key information towards differences in both genotypes towards resistance to PM. The transcriptomic signatures explored in this study will broaden our understanding towards molecular regulation of resistance to PM in hulless barley.

HbLFG1, a rubber tree (Hevea brasiliensis) lifeguard protein, can facilitate powdery mildew infection by regulating plant immunity

Powdery mildew causes substantial losses in crop and economic plant yields worldwide. Although powdery mildew infection of rubber trees (Hevea brasiliensis), caused by the biotrophic fungus Erysiphe quercicola, severely threatens natural rubber production, little is known regarding the mechanism by which E. quercicola adapts to H. brasiliensis to invade the host plant. In barley and Arabidopsis thaliana, lifeguard (LFG) proteins, which have topological similarity to BAX INHIBITOR-1, are involved in host plant susceptibility to powdery mildew infection. In this study, we characterized an H. brasiliensis LFG protein, HbLFG1, with a focus on its function in regulating defence against powdery mildew. HbLFG1 gene expression was found to be upregulated during E. quercicola infection. HbLFG1 showed conserved functions in cell death inhibition and membrane localization. Expression of HbLFG1 in Nicotiana benthamiana leaves and A. thaliana Col-0 was demonstrated to significantly suppress callose deposition induced by conserved pathogen-associated molecular patterns chitin and flg22. Furthermore, we found that overexpression of HbLFG1 in H. brasiliensis mesophyll protoplasts significantly suppressed the chitin-induced burst of reactive oxygen species. Although A. thaliana Col-0 and E. quercicola displayed an incompatible interaction, Col-0 transformants overexpressing HbLFG1 were shown to be susceptible to E. quercicola. Collectively, the findings of this study provide evidence that HbLFG1 acts as a negative regulator of plant immunity that facilitates E. quercicola infection in H. brasiliensis.

Crop Diversification to Control Powdery Mildew in Pea

Pea is a temperate grain legume cultivated worldwide that can be severely constrained by powdery mildew infection. Control by fungicides and the use of resistant cultivars is possible, but there is a growing interest in alternative control methods such as crop diversification, particularly in low input agriculture. The aim of this work was to assess the potential of intercropping pea with other crops and of pea cultivar mixtures for powdery mildew management on pea crop. Results show a reduction of powdery mildew on pea when intercropped by replacement at a 50:50 ratio with barley or with faba bean, but not when intercropped with wheat. A barrier effect seems to explain a major part of this decrease, especially in the pea/barley intercrop. This hypothesis was further supported by inoculated seedlings under controlled conditions, where powdery mildew infection on pea decreased with the distance to the inoculation point, this decrease being larger in the intercrop with barley than in the intercrop with wheat and in the pea monocrop. Powdery mildew was also reduced in the mixture of resistant and susceptible cultivars, with infection decreasing with the increasing proportions of the resistant one. Overall, this work shows that crop diversification may be a good strategy to reduce powdery mildew in pea.

Genome-wide identification and expression analysis of the B-box transcription factor gene family in grapevine (Vitis vinifera L.)

Background B-box (BBX) zinc-finger transcription factors play important roles in plant growth, development, and stress response. Although these proteins have been studied in model plants such as Arabidopsis thaliana or Oryza sativa, little is known about the evolutionary history or expression patterns of BBX proteins in grapevine (Vitis vinifera L.). Results We identified a total of 25 VviBBX genes in the grapevine genome and named them according to the homology with Arabidopsis. These proteins were classified into five groups on the basis of their phylogenetic relationships, number of B-box domains, and presence or absence of a CCT domain or VP motif. BBX proteins within the same group showed similar exon-intron structures and were unevenly distributed in grapevine chromosomes. Synteny analyses suggested that only segmental duplication events contributed to the expansion of the VviBBX gene family in grapevine. The observed syntenic relationships between some BBX genes from grapevine and Arabidopsis suggest that they evolved from a common ancestor. Transcriptional analyses showed that the grapevine BBX genes were regulated distinctly in response to powdery mildew infection and various phytohormones. Moreover, the expression levels of a subset of BBX genes in ovules were much higher in seedless grapevine cultivars compared with seeded cultivars during ovule development, implying a potential role in seed abortion. Additionally, VviBBX8, VquBBX15a and VquBBX29b were all located in the nucleus and had transcriptional activity except for VquBBX29b. Conclusions The results of this study establish the genome-wide analysis of the grapevine BBX family and provide a framework for understanding the biological roles of BBX genes in grapevine.

Evaluation of sainfoin accessions exposed to powdery mildew disease at four locations in Iran

In order to evaluate resistance of sainfoin (Onobrychis viciifolia) to powdery mildew, seeds of 19 accessions were collected from different parts of Iran and sown at 4 locations, i.e. Kheirabad, Khoramabad, Semirom and Tabriz, in 2014. Accessions were evaluated for powdery mildew severity index (DSI), forage dry matter yield (DM), dry matter digestibility (DMD) and crude protein (CP) and water soluble carbohydrate (WSC) concentrations over 4 years. Based on Duncan’s test, accessions 15353 and 3001 showed disease severity index lower than 25% and were nominated as resistant to powdery mildew. Accessions Oshnavieh and Polycross were considered semi-resistant due to their DSI ranging from 25 to 50%. Other accessions were considered susceptible because their DSI was higher than 50%. The resistant accessions (15353 and 3001) with average yields of 3,341 and 3,304 kg DM/ha were ranked as having high DM production, in addition to displaying high DMD plus high CP and WSC concentrations. Severity of powdery mildew infection was linked negatively with all 3 quality traits, i.e. DMD and CP and WSC concentrations. According to Eberhart/Russell regression results, stability of accessions 3001 and 15353 for DSI and DM yield was confirmed across 4 locations. We recommend the use of accessions 3001 and 15353 in future breeding programs to increase resistance to powdery mildew, while at least maintaining yield and quality attributes. Evaluation of other sources of sainfoin germplasm should continue to identify further resistant accessions.

“Macrobot”: An Automated Segmentation-Based System for Powdery Mildew Disease Quantification

Managing plant diseases is increasingly difficult due to reasons such as intensifying the field production, climatic change-driven expansion of pests, redraw and loss of effectiveness of pesticides, rapid breakdown of the disease resistance in the field, and other factors. The substantial progress in genomics of both plants and pathogens, achieved in the last decades, has the potential to counteract this negative trend, however, only when the genomic data is supported by relevant phenotypic data that allows linking the genomic information to specific traits. We have developed a set of methods and equipment and combined them into a “Macrophenomics facility.” The pipeline has been optimized for the quantification of powdery mildew infection symptoms on wheat and barley, but it can be adapted to other diseases and host plants. The Macrophenomics pipeline scores the visible powdery mildew disease symptoms, typically 5-7 days after inoculation (dai), in a highly automated manner. The system can precisely and reproducibly quantify the percentage of the infected leaf area with a theoretical throughput of up to 10000 individual samples per day, making it appropriate for phenotyping of large germplasm collections and crossing populations.