- Author: Kathy Keatley Garvey
Persimmons, asparagus, figs and other crops distantly related to native California plants attract fewer pests and diseases than the closer kin, and thus receive fewer pesticide treatments, according to a newly published article by two UC Davis-linked scientists in the Proceedings of the Natural Academy of Sciences (PNAS).
Co-authors Ian Pearse, research ecologist with the U.S. Geological Survey and a UC Davis alumnus, and Jay Rosenheim, UC Davis distinguished professor of entomology, analyzed the 2011-2015 state records of pesticide applications of 93 major California crops.
“We hypothesized that California crops that lack close relatives in the native flora will be attacked by fewer herbivores and pathogens and require less pesticide use,” said Rosenheim, a 32-year member of the UC Davis Department of Entomology and Nematology faculty and a newly elected fellow of the Entomological Society of America.
Rosenheim and Pearse examined the pesticide applications against arthropods, pathogens, and weed plants and compiled the data into a comprehensive analysis.
Their findings appear in the PNAS article, “Phylogenetic Escape from Pests Reduces Pesticides on Some Crop Plants,” published Oct. 12. “Phylogenetic relationship” refers to the relative times in the past that species shared common ancestors.
“In contrast, our study focuses on the roughly half of all herbivores and diseases that attack California crops and that are actually native to California. These organisms originally attacked members of the native California flora, but have now shifted to attack a novel host: the crop plant.”
However, “host shifts aren't always easy,” Rosenheim said. “It's relatively easy to shift to attack a close relative of a native host plant, but it's relatively hard to shift to attack a very different host plant.”
Said Pearse: “Our study shows that crops like dates, asparagus, figs, kiwis, or persimmons that are distantly related to native California plants--and thus separated by many million years of independent evolution-- are colonized by fewer pests and diseases.”
"The crops that require the most pesticide applications, Pearse said, "are those, like artichokes, blackberries, and sweet corn, that have close relatives in the Californian flora and are of high economic value per acre."
California's top agricultural crops include almonds, grapes, lettuce, strawberries, tomatoes and walnuts.
Rosenheim said persimmons are a good example “of the phenomenon we've studied: they have very, very few pests--almost zero in my experience--and that's probably because persimmons have no close relatives in the California native plant community.”
Pearse, a 2005 Fulbright scholar who received his doctorate in ecology from UC Davis in 2011, studying with Professor Rick Karban, joined the U.S. Geological Survey in Fort Collins in 2016. He focuses his research on invasive species and plant-insect interactions. Rosenheim researches insect ecology, with a focus on host-parasitoid, predator-prey, and plant-insect interactions, with direct applications to biological control.
“Pesticides are a ubiquitous (found everywhere) component of conventional crop production but come with considerable economic and ecological costs. We tested the hypothesis that variation in pesticide use among crop species is a function of crop economics and the phylogenetic relationship of a crop to native plants, because unrelated crops accrue fewer herbivores and pathogens. Comparative analyses of a dataset of 93 Californian crops showed that more valuable crops and crops with close relatives in the native plant flora received greater pesticide use, explaining roughly half of the variance in pesticide use among crops against pathogens and herbivores. Phylogenetic escape from arthropod and pathogen pests results in lower pesticides, suggesting that the introduced status of some crops can be leveraged to reduce pesticides.”
- Author: Kathy Keatley Garvey
Parents often try to predict the gender of their offspring, but is it possible to predict the sex of a cyst or sexually dimorphic nematode?
Yes, says plant nematologist Shahid Masood Siddique of the UC Davis Department of Entomology and Nematology, who helped develop and validate a strategy to predict the sex of cyst nematodes (round worms) in roots of a mustard family plant in the early stages of infestation.
The research paper, "Host Factors Influence the Sex of Nematodes Parasitizing Roots of Arabidopsis thaliana," published in a recent edition of the journal Plant, Cell and Environment, zeroes in on nematodes parasitizing a small flowering plant widely used in plant biology and known as "mouse-ear cress." Arabidopsis is a member of the mustard (Brassicaceae) family, which includes cabbage and radish. A native of Eurasia and Africa, mouse-ear cress is found throughout much of the United States and Canada.
"We identified the host genes and factors that influence environmental sexual determination of plant parasitic nematodes," said Siddique, the senior author of the paper and an assistant professor at UC Davis. He played a key role in designing and performing the research well as the written work.
The seven-member team, led by Florian Grundler of the University of Bonn, Germany, found that the nematodes that developed at the fastest rate during the first four to 5 days became females, "whereas those that grew slower became mainly males."
"Interestingly, a study by Müller et al. (1981) on comparative food consumption by male and female juveniles from roots of Brassica napus found that females consume about 29 times more food than males," the researchers wrote. "Based on our data and previous literature, we concluded that the difference in food consumption leads to the difference in body volume between the sexes."
The team also included scientists from Germany, Poland, and Pakistan. A DAAD grant from Germany funded the research.
"Plant-parasitic cyst nematodes induce hypermetabolic syncytial nurse cells in the roots of their host plants. Syncytia are their only food source. Cyst nematodes are sexually dimorphic, with their differentiation into male or female strongly influenced by host environmental conditions. Under favourable conditions with plenty of nutrients, more females develop, whereas mainly male nematodes develop under adverse conditions such as in resistant plants. Here, we developed and validated a method to predict the sex of beet cyst nematode (Heterodera schachtii) during the early stages of its parasitism in the host plant Arabidopsis thaliana. We collected root segments containing male-associated syncytia (MAS) or female-associated syncytia (FAS), isolated syncytial cells by laser microdissection, and performed a comparative transcriptome analysis. Genes belonging to categories of defence, nutrient deficiency, and nutrient starvation were over-represented in MAS as compared with FAS. Conversely, gene categories related to metabolism, modification, and biosynthesis of cell walls were over-represented in FAS. We used β-glucuronidase analysis, qRT-PCR, and loss-of-function mutants to characterize FAS- and MAS-specific candidate genes. Our results demonstrate that various plant-based factors, including immune response, nutrient availability, and structural modifications, influence the sexual fate of the cyst nematodes."
Siddique, who joined the UC Davis faculty in March, focuses his research on basic as well as applied aspects of interaction between parasitic nematodes and their host plants. "The long-term object of our research is not only to enhance our understanding of molecular aspects of plant–nematode interaction but also to use this knowledge to provide new resources for reducing the impact of nematodes on crop plants in California."
Plant-parasitic nematodes are microscopic worms that extract water and nutrients from such host plants as wheat, soybeans, sugar beets and bananas. “They're one of the most destructive agricultural pests,” Siddique says. “The agricultural losses due to plant-parasitic nematodes reach an estimated $80 billion. The high impact of plant parasitic nematodes in economically important crops is not only due to the direct damage but also because of the role of some species as virus vectors.”