Nutrient regulation of the saprotroph to parasite transition in Pochonia chlamydosporia a soil microbial inoculant for nematode control

Plant parasitic nematodes feed on plant roots, stunt their growth and make root systems less efficient at withdrawing nutrients and water from soil. Yields of nematode-infected crops are reduced and annual losses worldwide are estimated to cost US$100b, despite control measures. Nematodes significantly reduce the water use efficiency of crops and climate change impacts predicted for sub-Saharan Africa suggest that their damage to crops will significantly increase. Root-knot nematodes (Meloidogyne spp.) are the major nematode pests of most tropical crops and may cause total crop failures on susceptible crops in Africa. In intensive cropping systems growers depend on plant resistance and chemicals to manage nematode pests. Nematicides are some of the most toxic products used in crop protection and their use has been banned in several European countries due to environmental concerns and public pressures to reduce dependence on agro-chemicals. There is an urgent need to develop other control methods to replace current nematicides. This proposal builds on a) collaborative research at Rothamsted and the Centro Nacional de Sanidad Agropecuaria, Havana, Cuba, which has led to the development of a rhizosphere-inhabiting fungus, Pochonia chlamydosporia, as a biological control agent and b) selected biotypes of P. chlamydosporia from Kenya evaluated in previous DFID funded research (Crop Protection Programme Project R8296). The fungus grows saprotrophically on the surface of plant roots and switches to become a parasite on contact with nematode eggmasses produced by Meloidogyne spp. It destroys the eggs that contain the infective juveniles, which give rise to the next nematode generation; there may be several generations on a crop but single applications of the fungus significantly reduce nematode infestations. There is no simple relationship between the abundance of the fungus in soil and its parasitic activity, which is much affected by the nutritional status of the fungus. Organic soil amendments have been used to greatly increase the abundance of the fungus in soil but such treatments do not necessarily increase the levels of biological control. We will study the nutritional factors that affect the rates of fungal parasitism of nematode eggs. We have identified, sequenced and cloned the VCP1 gene from P. chlamydosporia, which encodes an alkaline serine proteinase involved in the initial stages of the infection process and is an indicator of the beginning of the parasitic phase in the fungus. The influence of nutritional factors on the expression of this gene will be used to identify factors that affect the onset of the parasitic phase, essential for biological control. This basic research on the effects of fungal nutrition on biological control activity will be complemented by studies at the University of Nairobi on the effects on fungal abundance and parasitic activity of selected soil amendments with defined carbon:nitrogen ratios and their extracts. The link will provide opportunities to work with local nematode infestations and types of soil amendments in typical nutrient-depleted soils. Colleagues in the University have the facilities and expertise to conduct the research and to suggest modifications to the experimentation conducted at Rothamsted. Both the research groups at Rothamsted and the University of Nairobi are part of the Nematology Initiative in East and Southern Africa (NIESA), supported by the Gatsby Charitable Foundation, which brings together nematologists within the UK and in Kenya, Malawi, Tanzania, Uganda and Zimbabwe, NIESA forms a network with close links to local growers and entrepreneurs and will ensure an established uptake pathway for the outputs of the project.

Root-knot nematodes (Meloidogyne spp.) are major nematode pests of most tropical crops, making roots less efficient at withdrawing nutrients and water from soil, sometimes causing the total failure of crops grown by resource-poor farmers in Africa. Nematicides are some of the most toxic products used in crop protection, and are inappropriate or too expensive for use on most crops in Africa and there is an urgent need for new methods of nematode management. The fungus Pochonia chlamydosporia is a promising biological control agent. It colonises the surface of plant roots and switches to become a parasite on contact with nematode eggmasses produced by Meloidogyne spp., destroying the eggs. There is no simple relationship between fungal abundance in soil and parasitic activity, which is significantly affected by nutrition. Organic soil amendments used to increase abundance of the fungus do not necessarily increase biological control. We will study the nutritional factors that affect fungal abundance and parasitism (University of Nairobi) and the effects of nutrition on fungal gene expression on egg parasitism in vitro (Rothamsted). The VCP1 gene from P. chlamydosporia expresses an alkaline serine proteinase involved in the initial stages of egg infection, indicating the beginning of the parasitic phase. We have sequence data and preliminary information on the regulation of this gene. We can measure VCP1 activity using colorimetric assays and gene activity using quantitative RT-PCR. The influence of nutritional factors, including root exudates from nematode-infected plants, on the expression of this and other genes will be studied to determine their role in the onset of the parasitic phase, essential for biological control. This basic research will be complemented by studies at the University of Nairobi on the effects of selected soil amendments with defined carbon:nitrogen ratios and their extracts on fungal abundance and parasitic activity.