Transgenic virus resistance in cultivated squash affects pollinator behaviour

Plant Virus Impacts on Yield and Plant-Pollinator Interactions Are Phylogenetically Modulated Independently of Domestication in Cucurbita spp

Plant defenses are conserved among closely related species, but domestication can alter host genotypes through artificial selection with potential losses in host defenses. Therefore, both domestication and host phylogenetic structure may influence plant virus infection outcomes. Here, we examined the association of phylogeny and domestication with the fitness of infected plants. We inoculated three pairs of domesticated and wild/noncultivated squash (Cucurbita spp.) with a combination of two viruses commonly found to coinfect cucurbits, zucchini yellow mosaic virus and squash mosaic virus, and recorded fitness traits related to flowers, pollination, fruit, and seed viability in the field over 2 separate years. In an additional field experiment, we recorded the relative abundance of both viruses via RT-qPCR. We found a gradient of susceptibility across the six tested lineages, and phylogenetic structure, but not domestication, contributed to differences in infection outcomes and impacts on several fitness traits, including fruit number, fruit weight, and germination. Plant virus infection also impacted the quantity and quality of floral rewards and visitation rates of specialist bee pollinators. There were no detectable differences in viral load between the six host taxa for either virus individually or the ratio of zucchini yellow mosaic virus to squash mosaic virus. Our results highlight the importance of phylogenetic structure in predicting host susceptibility to disease across wild and domesticated plants and the ability of several hosts to maintain fitness in the field despite infection. Broader consequences of plant pathogens for beneficial insects, such as pollinators, should also be considered in future research.

The pollen virome: A review of pollen-associated viruses and consequences for plants and their interactions with pollinators

The movement of pollen grains from anthers to stigmas, often by insect pollinator vectors, is essential for plant reproduction. However, pollen is also a unique vehicle for viral spread. Pollen-associated plant viruses reside on the outside or inside of pollen grains, infect susceptible individuals through vertical or horizontal infection pathways, and can decrease plant fitness. These viruses are transferred with pollen between plants by pollinator vectors as they forage for floral resources; thus, pollen-associated viral spread is mediated by floral and pollen grain phenotypes and pollinator traits, much like pollination. Most of what is currently known about pollen-associated viruses was discovered through infection and transmission experiments in controlled settings, usually involving one virus and one plant species of agricultural or horticultural interest. In this review, we first provide an updated, comprehensive list of the recognized pollen-associated viruses. Then, we summarize virus, plant, pollinator vector, and landscape traits that can affect pollen-associated virus transmission, infection, and distribution. Next, we highlight the consequences of plant-pollinator-virus interactions that emerge in complex communities of co-flowering plants and pollinator vectors, such as pollen-associated virus spread between plant species and viral jumps from plant to pollinator hosts. We conclude by emphasizing the need for collaborative research that bridges pollen biology, virology, and pollination biology.

Populational survey of arthropods on transgenic common bean expressing the rep gene from Bean golden mosaic virus

Genetically modified (GM) crops is considered the fastest adopted crop technology in the history of modern agriculture. However, possible undesirable and unintended effects must be considered during the research steps toward development of a commercial product. In this report we evaluated effects of a common bean virus resistant line on arthropod populations, considered as non-target organisms. This GM bean line (named M1/4) was modified for resistance against Bean golden mosaic virus (BGMV) by expressing a mutated REP protein, which is essential for virus replication. Biosafety studies were performed for a period of three years under field conditions. The abundance of some species was significantly higher in specific treatments in a particular year, but not consistently different in other years. A regular pattern was not observed in the distribution of insects between genetically modified and conventional treatments. Data analyses showed that minor differences observed can be attributed to random variation and were not consistent enough to conclude that the treatments were different. Therefore the present study indicates that the relative abundance of species are similar in transgenic and non-transgenic fields.

Effects of virus on plant fecundity and population dynamics

Microorganisms are ubiquitous and thought to regulate host populations. Although microorganisms can be pathogenic and affect components of fitness, few studies have examined their effects on wild plant populations. As individual traits might not contribute equally to changes in population growth rate, it is essential to examine the entire life cycle to determine how microorganisms affect host population dynamics. In this study, we used data from common garden experiments with plants from three Cucurbita pepo populations exposed to three virus treatments. These data were used to parameterize a deterministic matrix model, which allowed us to estimate the effect of virus on components of fitness and population growth rate. Virus did not reduce fruit number, but population growth rates varied among virus treatments and wild C. pepo populations. The effect of virus on population growth rate depended on virus species and wild C. pepo population. Contributions of life-history transitions and life-history traits to population growth rates varied among populations and virus treatments. However, this population-virus interaction was not evident when examining individual components of fitness. Thus, caution must be used when interpreting the effects of changes in individual traits, as single traits do not always predict population-level change accurately.

Minimising losses caused by Zucchini yellow mosaic virus in vegetable cucurbit crops in tropical, sub-tropical and Mediterranean environments through cultural methods and host resistance

Between 2006 and 2009, 10 field experiments were done at Kununurra, Carnarvon or Medina in Western Australia (WA) which have tropical, sub-tropical and Mediterranean climates, respectively. These experiments investigated the effectiveness of cultural control measures in limiting ZYMV spread in pumpkin, and single-gene resistance in commercial cultivars of pumpkin, zucchini and cucumber. Melon aphids (Aphis gossypii) colonised field experiments at Kununurra; migrant green peach aphids (Myzus persicae) visited but did not colonise at Carnarvon and Medina. Cultural control measures that diminished ZYMV spread in pumpkin included manipulation of planting date to avoid exposing young plants to peak aphid vector populations, deploying tall non-host barriers (millet, Pennisetum glaucum) to protect against incoming aphid vectors and planting upwind of infection sources. Clustering of ZYMV-infected pumpkin plants was greater without a 25m wide non-host barrier between the infection source and the pumpkin plants than when one was present, and downwind compared with upwind of an infection source. Host resistance gene zym was effective against ZYMV isolate Knx-1 from Kununurra in five cultivars of cucumber. In zucchini, host resistance gene Zym delayed spread of infection (partial resistance) in 2 of 14 cultivars but otherwise did not diminish final ZYMV incidence. Zucchini cultivars carrying Zym often developed severe fruit symptoms (8/14), and only the two cultivars in which spread was delayed and one that was tolerant produced sufficiently high marketable yields to be recommended when ZYMV epidemics are anticipated. In three pumpkin cultivars with Zym, this gene was effective against isolate Cvn-1 from Carnarvon under low inoculum pressure, but not against isolate Knx-1 under high inoculum pressure, although symptoms were milder and marketable yields greater in them than in cultivars without Zym. These findings allowed additional cultural control recommendations to be added to the existing Integrated Disease Management strategy for ZYMV in vegetable cucurbits in WA, but necessitated modification of its recommendations over deployment of cultivars with resistance genes.