Tripartite interactions among soybean vein necrosis orthotospovirus, vector thrips and soybean plants
Open Access
- Author:
- Hameed, Asifa
- Graduate Program:
- Entomology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 18, 2020
- Committee Members:
- Edwin G. Rajotte, Dissertation Advisor/Co-Advisor
Edwin G. Rajotte, Committee Chair/Co-Chair
Cristina Rosa, Committee Chair/Co-Chair
Ruud Schilder, Committee Member
Surrinder Chopra, Outside Member
Cheryle A. O’ Donnell, Special Member
Cristina Rosa, Dissertation Advisor/Co-Advisor
Gary Felton, Program Head/Chair - Keywords:
- Soybean vein necrosis virus
N. variabilis
thrips
CLSM
Ovipositor
Chemical ecology
life table
virus infection
Pakistan
Soybean plant physiology - Abstract:
- Soybean is an important food, forage, oil seed and potential biodiesel crop, exported throughout the world mainly by three leaders- Brazil, United States and Argentina (Shahbande, 2020). During 2019-2020, the export volume of soybeans by Brazil, United States and Argentina was 84, 45.59, and 8.0 million metric tonnes respectively (Shahbande, 2020). The rest of the world purchases this valuable commodity for food, oil and feed purposes. Orthotospoviruses cause billions of dollars in losses to many agricultural commodities around the world. Soybean vein necrosis virus (SVNV) is one of the eight economically important seed and vector transmitted viruses presently infecting soybeans in the United States, Canada and Egypt. Being a seed and vector transmitted virus, SVNV poses a risk of virus propagation to other countries as well as reduction in oil quality and quantity of soybeans. The purpose of this thesis is to provide information to the farmers, scientists and others about the effect of SVNV on vectors and soybean plants. The information thus obtained could be utilized by IPM specialists to create strategies against the virus and vector, by better understanding the chemical ecology, nutritional chemistry of virus infected plants and vector biology, including feeding preference, and population changes. This thesis is comprised of seven chapters. In chapter 1, I described the literature on the geographical dispersal of the SVNV and its vectors species throughout the world, reservoir host plants of the vector and virus, disease diagnostics tools for SVNV, effect of SVNV on the seed qualitative parameters and management perspectives of the vectors. In chapter 2, I described the duration of each larval and pupal instar of SVNV infected and SVNV uninfected thrips and established the life table of soybean thrips infected with SVNV. I found that SVNV infected thrips had increased fertility and longevity. I postulated that SVNV changed the plant nutritional chemistry or defense pathways which ultimately improved the survival of soybean thrips. The information gained through this chapter would be useful to design the experiments to understand the transcriptomics and proteomics of the virus infected plants and vectors and to assess if modulation in the insect hormones ecdysone and juvenile hormone occur. Chapter 3 describes the external and internal genitalia of female thrips. I found similarities and differences with the Bode (1975) description of female ovipositor of Thrips physapus. Overall, both the T. physapus and Neohydatothrips variabilis had an ADR gland (appendage gland) which opens into the ovipositor. Secretions from this gland might have some significant role in thrips biology and future research would provide valuable information about that. I found that the N. variabilis female lays eggs along the sides of veins. Chapter 4 describes the alternative host reservoirs of thrips vector species in Pennsylvania and the overwintering behavior of N. variabilis, role of weather factors on the thrips population dynamics, thrips abundance, preference and non-preference for different cultivars of soybeans, effect of thrips on the protein, carbohydrate, fiber and oil content in different soybean cultivars, effect of virus on the plant physiology and morphology. Under field conditions thrips on average were less than 2 per plant but their numbers increased rapidly in the month of August, when rainfall is abundant and humidity is high. I also observed thrips preferred feeding and oviposition sites (near the leaf veins in upper canopy) which would help the IPM specialist to scout thrips number. On this basis I suggest scouting for thrips numbers in the month of July and August. Under controlled conditions, thrips numbers become much higher and have a negative impact on plants. Plant photosynthesis was also affected by virus presence under growth chamber conditions. Since SVNV is potentially moving along with seeds throughout the world, I wanted to determine if SVNV is present in Pakistan. To do so, I interviewed many farmers and scientists to determine their awareness of SVNV. I found that in Pakistan farmers and scientists were not aware of this disease by the name of soybean vein necrosis (SVND), but the color photographs of SVNV infected leaves helped them to identify its presence. There are some fundamental differences between the production of soybean in the US and Pakistan and between the timing of symptom appearance in the two countries. In the United States, even though soybean is planted in May, virus symptoms appear in August (northern states PA, Indiana, Iowa) while in Pakistan, soybean is planted in July and symptoms were evident in August, just one month after crop planting. In Pakistan, a very high diversity of thrips fauna is present, and due to the tropical climate, no hibernation or overwintering of thrips takes place. Thrips remain active throughout the year, and they shift to soybeans when the crop becomes available, affecting its quality and productivity. Another observation was that scientists and farmers were relying on the heavy use of insecticides to control the pests on soybean crop, which tended to mask the underlying problems. In addition, soybean was cultivated along with mung beans and mash beans. Mung beans and mash beans are considered the diet of poor people in Asia and mung beans can host SVNV. While N. variabilis was not found by me in Pakistan, other species of thrips were found on soybeans and may serve as SVNV vectors. I also found SVNV in soybean plants and thrips in Pakistan. I confirmed this through ELISA and real time PCR. In Pakistan, soybean cultivars vary in their susceptibility or resistance to SVNV. In Pakistan farmers in the Punjab region location do not cultivate much soybean. However, we found that most farmers in Khyber Pakhtunkhwa (KPK) region were growing soybeans. A soybeans ancestor, Glycine soja, is a traditional crop of Kashmir in Pakistan. Farmers have the ability to grow them for livestock and feed purposes including human consumption. That may be a reason people of KPK warmly accepted the introduction of this crop, but not in Punjab, Balochistan and Sindh provinces of Pakistan. My research in Pakistan provides a valuable information that SVNV is not only present in United States, Canada and Egypt but is also present in Pakistan. Further research on the SVNV isolates from Pakistan and the world would clarify the similarities and origin of SVNV. Another important aspect of SVNV is its epidemiology. The virus infected thrips move between SVNV infected and healthy plants. Exactly how thrips choose to settle on the plants is mediated by olfactory, gustatory and tactile cues. I determined the volatile profile of SVNV inoculated and naturally infected plants infested with thrips. I also analyzed free essential, non-essential amino acids and metabolites, other organic acids and lipids in different plant niches. I found that virus infection reduces the essential free amino acids in the plant leaf but in SVNV infected via thrips & thrips infested plants, the non-essential and essential amino acids were reduced. I conclude that SVNV infected plants via mechanical inoculation emit volatile which attract vectors for oviposition, and that the progeny leaves the plants due to poor nutritional quality. The volatile profile of the upper canopy leaves can be used to attract soybean thrips to yellow sticky traps and hence increase the efficacy of pest management programs. However, the individual role of each compound needs to be determined through Y-tube tests to determine what compound or compounds could be responsible for this preference. Overall, my thesis generates information for the scientists and the farming community about SVNV, its vectors and plant interactions which could be utilized for further pest management.