Plant parasitic nematodes: the effect of lolines.

Abstract

Grass endophytes live their entire life cycle within the aerial portion of the grass host, with which they form a defensive mutualism. The endophyte which resides intercellularly within the grass, synthesizes an array of alkaloids that collectively deter mammalian, insect and nematode herbivory. Reciprocally the endophyte profits directly from the host’s provision of nutrients, water, isolation from competition and guarantee of vertical transmission to the next host generation. The discovery by Bacon et al., (1977) of a link between livestock toxicity and endophyte presence in pasture initially resulted in the selection for nil endophyte grasses. However it was soon discovered that production and persistence of nil endophyte grass stands were decidedly inferior to endophyte-infected stands. Further research revealed that there was much variation in the alkaloids and respective functions, produced within and between species of Neotyphodium endophytes. Some endophytes were shown to confer resistance to an array of insect pests without extending any ill effect to livestock. Since then these endophytes, referred to hereafter as ‘novel’ endophytes have been selected and bred into grass with high agronomic value However concerns have been raised regarding persistence of novel endophyte infected tall fescue stands under plant parasitic nematode pressure. These nematodes through feeding on and burrowing through young root tissue affect the water uptake capability of the grass roots. This compromises plant persistence under drought conditions particularly on free draining sandy soils. This problem warrants investigation of all grass-endophyte associations and alkaloid interactions in a bid to identify such an association that would confer resistance to this pest. Three glasshouse pot trials were conducted at Lincoln University, Canterbury, NZ. The objective of the trials were to (1) investigate the relationship between the root concentrations of Neotyphodium produced alkaloid (loline) and nematode parasitism; (2) To investigate the effect of nematode parasitism on plant loline synthesis as a defensive response mechanism. (3) To investigate whether lolines leached from endophyte-infected, dead grass material is taken up by neighbouring plants. Due the unfortunate necessity to pool replications, results attained from this trial were merely indicative. The results however did suggest that there is an inversely proportional relationship between nematode presence in roots and total root loline concentrations. Additionally the results suggested that root loline concentrations increased with trimming and nematode herbivory. There no evidence to suggest that loline leached from endophyte-infected dead grass material were taken up by other members of the plant community. The suggestive evidence presented in the results of the first two trials holds significant implications for New Zealand and International pastoral agriculture if shown by further research to be accurate. Loline producing endophytes such as Neotyphodium uncinatum can now be bred or introduced into prominent pastoral grasses Festuca arundinacea Shreb. and Lolium perenne L. This would extend the nematoxic properties of loline, which confers no ill effect to grazing livestock, to these important pasture constituents.