Rice Resistance Buffers against the Induced Enhancement of Brown Planthopper Fitness by Some Insecticides

The brown planthopper, Nilaparvata lugens (Stål)[BPH], is a damaging pest of rice in Asia. Insecticides and rice varietal resistance are widely implemented BPH management practices. However, outbreaks of BPH have been linked to excessive insecticide use—challenging the compatibility of these two management practices. IR62 is a variety with resistance against BPH, the whitebacked planthopper, Sogatella furcifera Horváth [WBPH], and the green leafhopper, Nephotettix virescens (Distant)[GLH]. We compared BPH responses to IR62 and to the susceptible variety IR64 treated with buprofezin, carbofuran, cartap hydrochloride, cypermethrin, deltamethrin, fipronil, or thiamethoxam + chlorantraniliprole. In greenhouse bioassays, cypermethrin, fipronil and thiamethoxam + chlorantraniliprole reduced egg laying on both varieties, and, together with buprofezin, reduced nymph survival to zero. Buprofezin, carbofuran, and cartap hydrochloride stimulated egg laying, and carbofuran increased nymph biomass, but these effects were reduced on IR62. Planthopper populations were ten times higher on deltamethrin-treated rice than untreated rice in a screenhouse experiment. Host resistance failed to buffer against this insecticide-induced resurgence in BPH and WBPH. However, IR62 reduced the effect in GLH. Rice treated with cypermethrin and fipronil had reduced yields compared to untreated controls, suggesting possible phytotoxic effects. We found little evidence of synergies between the two management practices; but host resistance did buffer against the undesirable effects of some insecticides.

Spatiotemporal Changes in Varietal Resistance to Wheat Yellow Rust in France Reveal an Increase in Field Resistance Level During the Period 1985–2018

Monitoring spatiotemporal changes in varietal resistance and understanding its drivers seem essential to managing plant diseases but require having access to the genetic basis of disease resistance and to its deployment. In this study, we focused on yellow rust (Puccinia striiformis f. sp. tritici ) for three decades in France, by using field adult plant resistance levels, Yr race-specific resistance genes of varieties, presence of Puccinia striiformis f. sp. tritici pathotypes and their virulence profiles, and systematic surveys of the acreages of bread wheat varieties available at a yearly survey time and at a district level. Based on these data, we studied spatiotemporal changes in varietal resistance over the period from 1985 to 2018 in 54 French administrative districts (hereafter “departments”) by using a set of relevant indicators weighted by the relative acreage proportion of the varieties sown at the department level. Our analyses revealed an increase in varietal resistance over decades that would be due to the accumulation of both quantitative resistance and different race-specific resistance genes. We suggest that, beyond breeders, several actors, including examination offices, agricultural advisory services, and farmers, may have had a substantial influence on these spatiotemporal changes, promoting more resistant varieties and the rapid replacement of newly susceptible varieties by still resistant ones at the beginning of each epidemic.

A Simple Method for the Acquisition and Transmission of Brassica Yellows Virus from Transgenic Plants and Frozen Infected Leaves by Aphids

Brassica yellows virus (BrYV) is a tentative species of the genus Polerovirus, which occurs widely, and mostly damages Brassicaceae plants in East Asia. Because BrYV cannot be transmitted mechanically, an insect-based transmission method is required for further virus research. Here, a reliable and unrestricted method is described, in which non-viruliferous aphids (Myzus persicae) acquired BrYV from transgenic Arabidopsis thaliana, harboring the full-length viral genome germinated from seeds and its frozen leaves. The aphids then transmitted the virus to healthy plants. There was no significant difference in acquisition rates between fresh and frozen infected leaves, although the transmission rate from frozen infected leaves was lower compared to fresh infected leaves. This simple novel method may be used to preserve viral inocula, evaluate host varietal resistance to BrYV, and investigate interactions among BrYV, aphids, and hosts.

Wheat Blast: A Disease Spreading by Intercontinental Jumps and Its Management Strategies

Wheat blast (WB) caused by Magnaporthe oryzae pathotype Triticum (MoT) is an important fungal disease in tropical and subtropical wheat production regions. The disease was initially identified in Brazil in 1985, and it subsequently spread to some major wheat-producing areas of the country as well as several South American countries such as Bolivia, Paraguay, and Argentina. In recent years, WB has been introduced to Bangladesh and Zambia via international wheat trade, threatening wheat production in South Asia and Southern Africa with the possible further spreading in these two continents. Resistance source is mostly limited to 2NS carriers, which are being eroded by newly emerged MoT isolates, demonstrating an urgent need for identification and utilization of non-2NS resistance sources. Fungicides are also being heavily relied on to manage WB that resulted in increasing fungal resistance, which should be addressed by utilization of new fungicides or rotating different fungicides. Additionally, quarantine measures, cultural practices, non-fungicidal chemical treatment, disease forecasting, biocontrol etc., are also effective components of integrated WB management, which could be used in combination with varietal resistance and fungicides to obtain reasonable management of this disease.

First Report of Leaf Blight of Sugar Beet (Beta vulgaris) Caused by Sclerotinia sclerotiorum in Minnesota, U.S.A.

Minnesota is the top sugar beet (Beta vulgaris L.) producing state in the United States. In 2020, sugar beet plants were observed for the first time in which the two to three oldest leaves had light brown to dark brown necrotic leaf lesions that eventually became yellow or brown and died but remained attached to the plant. Morphological data and sequences of internal transcribed spacer regions identified the pathogen as Sclerotinia sclerotiorum. Because over 90% of the plants in identified fields were infected it was difficult to quantify loss in yield or quality caused by this disease. All fields with symptomatic plants had soybean or edible beans in the rotation. One field planted to several different varieties indicated that all the varieties were symptomatic. It will be useful to determine any economic loss caused by S. sclerotiorum and any known varietal resistance to this pathogen.

Pectobacterium brasiliense (soft rot and blackleg of ornamentals and potato).

Pectobacterium brasiliense is a bacterial pathogen primarily infecting potato and other vegetables and ornamentals. The earliest reports of the bacterium causing disease were from Brazil in 2004 (El-Tassa and Duarte, 2004; Duarte et al., 2004). This pathogen was reported for the first time in Europe (Belgium) in 2012 (van der Wolf et al., 2017). Since then, the pathogen has been reported in many regions of Europe, Asia, Africa, Australia, North and South America. The bacterium has adapted itself to a wide range of temperatures and host species, thus it is considered a culprit for significant losses in China, South Africa, Brazil, Netherlands, Switzerland and UK (Meng et al., 2017; van der Wolf et al., 2017). Symptoms caused by P. brasiliense are indistinguishable from other soft rot Pectobacterium and Dickeya, therefore it is impossible to identify this species on the basis of field and laboratory symptoms. Unfortunately, there is no evidence of curative measures and varietal resistance (in cultivated potatoes) against this group of bacteria, so farmers rely on seed certification, exclusion and sanitation to mitigate its worst effects.

Pectobacterium brasiliense (soft rot and blackleg of ornamentals and potato).

Pectobacterium brasiliense is a bacterial pathogen primarily of potato and other vegetables and ornamentals. The earliest reports of the bacterium causing disease were from Brazil in 2004 (El-Tassa and Duarte, 2004). This pathogen was reported for the first time in Europe (Belgium) in 2012 (van der Wolf et al., 2017). Since then, the pathogen has been reported in many regions of Europe, Asia, Africa, Australia, North and South America. The bacterium has adapted itself to a wide range of temperatures and host species, thus it is considered a culprit for significant losses in China, South Africa, Brazil, Netherlands, Switzerland and UK (Meng et al., 2017; van der Wolf et al., 2017). Symptoms caused by P. brasiliense are indistinguishable from other soft rot Pectobacterium and Dickeya, therefore it is impossible to identify this species on the basis of field and laboratory symptoms. Unfortunately, there is no evidence of curative measures and varietal resistance (in cultivated potatoes) against this group of bacteria, so farmers rely on seed certification, exclusion and sanitation to mitigate its worst effects.

Plasmodiophora brassicae (club root).

Plasmodiophora brassicae is a root-infecting protist pathogen that causes clubroot disease in brassica species. The organism is soil-borne and has long-lived resting spores that can survive in soil for more than 15 years. Local spread of motile zoospores can be facilitated by wet conditions but most dispersal of the pathogen is through the movement of infested soil. P. brassicae has a wide host range in the brassica family including numerous weed species. Control of the disease is difficult but clubroot can be managed by a combination of crop rotation, varietal resistance, improved agronomic practice such as improved drainage and the application of lime of related products to raise pH which can limit the effects of the disease. There are currently no effective fungicides for the widespread control of clubroot. Yield losses range from 10 to 15% but can exceed 50% under disease conducive environmental conditions.