Biotechnology of Endophytic Fungi of Grasses

Charles W. Bacon

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351087223
• Edition: 1
• Topic: Medicine
• Subtopic: Biotechnology in Medicine

This book considered the biological, ecological, toxicology, and chemical aspects of research topics as they relate to endophytes of grasses. Several chapters reflect the very pragmatic applications of endophytes and endophyte-infected grasses. Other chapters offer future applications for endophytes and are therefore discussed from theoretical viewpoints. This book contains the collective writings of an international group of experts on fungal endophytes of grasses, all of whom are directed toward, understanding, creating, and exploiting the positive aspects of endophytes. With this book, we are attempting to stimulate and facilitate future explorations of the grass endophytes.

Section V1

Utilization of Endophyte-Infected Grasses Based on Agronomic Characteristics

Chapter 12

Utilization of Endophyte-lnfected Perennial Ryegrasses for Increased Insect Resistance

Daryl D. Rowan and Garrick C. M. Latch

CONTENTS

I.	Introduction
II.	Metabolites Involved in Insect Resistance
	A.	Indole Diterpenes
	B.	Ergot Alkaloids
	C.	Peramine
III.	Resistance to the Argentine Stem Weevil
	A.	Adult-Stage Resistance
	B.	Larvae-Stage Resistance
	C.	Resistance in Seeds and Seedlings
IV.	Other Insect Species Affected by Endophyte-lnfected Ryegrass
	A.	Fall Army worms
	B.	Aphids
	C.	Other Insects and Vertebrates
V.	Expressions of Endophyte-Mediated Interactions
	A.	Species Variation
	B.	Acute Toxicity
	C.	Overcoming Resistance
VI.	Factors Affecting Endophyte-Induced Insect Resistance
	A.	Biotic Influences
	B.	Abiotic Influences
VII	Selection of Endophyte Strains for Insect Resistance
	A.	Nonalkaloid-Producing Isolates
	B.	Natural and Genetically Altered Alkaloid-Producing Isolates
VIII.	Conclusion
References

I. INTRODUCTION

Insect resistance associated with endophyte infection of a grass was first reported by Prestidge et al.⁸⁶ in 1982 after regrowth of grass in plots of endophyte-free perennial ryegrass (Lolium perenne L.) was observed to be greatly inferior to that in endophyte-infected plots. Inspection of the endophyte-free plants revealed they were heavily infested with Argentine stem weevil (Listronotis bonariensis) and that the majority of tillers had died as a result of feeding by stem-weevil larvae. Little damage from the Argentine stem weevil was observed in the plots containing endophyte-infected perennial ryegrass. This initial observation of the protection afforded to a grass by its endophyte aroused much interest and provided the explanation for the maternally inherited resistance of turf ryegrasses to sod web worm (Crambus sp.) subsequently reported by Funk et al.⁴⁰

Many other species of insects have now been found to be adversely affected by the presence of endophytes in ryegrasses and other grasses. Latch⁵⁵ lists some 24 diverse insect species adversely affected by the presence of endophytes in perennial ryegrass and tall fescue (Festuca arundinacea Schreb.). New records of insects affected by endophytes in ryegrass, since this publication, are listed in Table 1. A number of recent reviews have considered the insect resistance of endophyte-infected grasses, from agronomic or ecological perspectives.^{21, 22, 23, 23,35,78,104} The use of fungal endophytes to render plants resistant to insect herbivores is both novel and timely in a world that is becoming increasingly aware of pesticide pollution. Not only can the use of pesticides be reduced on endophyte-infected turf grass species, but grasses can be protected from their insect herbivores in pastures and conservation areas where it is not generally economic to apply insecticides.

Table 1 Insects reported to be affected by endophyte-infected ryegrass and tall fescue subsequent to the list given by Latch⁵⁵

Insect	Reference
Abacarus hystrix (cereal rust mite)	38
Agrotis infusa (common cutworm)	87
Aphodius tasmaniae (blackheaded cockchafer)	87
Costelytra zealandica (grass grub)	76
Cyclocephala lurida (southern masked chafer)	80
Draeculocephala spp. (leafhopper)	67
Exitianus exitiosus (leafhopper)	67
Graminella nigrifrons (leafhopper)	67
Heteronychus arator (black beetle)	6
Locusta migratoria (migratory locust)	60
Mythimna convecta (common armyworm)	87
Parapediasia teterrella (bluegrass webworm)	53
Persectania ewingii (southern armyworm)	87
Philobota productella (pasture tunnel moth)	87
Prosapia bicincta (froghopper)	67
Sipha flava (sugarcane aphid)	41
Teleogryllus commodus (black field cricket)	87
T. oceanicus (Queensland field cricket)	87

Most of the research on insect behavior and the chemistry of toxins and antifeedants in endophyte-infected grasses has been done with ryegrass and its herbivores. This chapter will focus on our current knowledge of the insect resistance of endophyte-infected perennial ryegrass and, to a lesser extent, on other species commonly used in pastures and in turf culture. The chemical mechanisms of insect resistance in ryegrass will be discussed, as will other biotic and abiotic factors known to influence endophyte-enhanced pest resistance. Strategies to optimize the beneficial effects of endophytes in pasture and turf environments will be discussed in the light of current experience using endophyte-infected perennial ryegrass as a model system.

II. METABOLITES INVOLVED IN INSECT RESISTANCE

Before discussing the specific endophyte interactions with particular insect species, it is useful to summarize the range of fungal metabolites identified in endophyte-infected grasses and for which specific anti-insect properties have been demonstrated. To date, three classes of fungal metabolites, the indole diterpenes,¹⁶ the ergot alkaloids,⁹⁶ and peramine,⁹³ have been implicated as being responsible for the insect resistance of endophyte-infected perennial ryegrass. The loline alkaloids, important for insect resistance in endophyte-infected tall fescue,^34,88,99 also occur in some other Lolium species,⁷⁴ but are not normally found in perennial ryegrass (but see Huizing et al.⁵⁰). Loline alkaloids are produced, however, in perennial ryegrass artificially infected with the endophyte Acremonium coenophialum, which normally infects tall fescue.⁹⁹ Such artificial endophyte–grass combinations may prove useful as a means of incorporating new insect-active compounds into ryegrass.

Figure 1 Indole diterpene mycotoxins identified in endophyte-infected ryegrass.

A. INDOLE DITERPENES

The indole diterpene mycotoxins consist of a diverse range of chemical structures that share a common biosynthetic origin, being formed from a tryptophan-derived indole fragment and a 20-carbon isoprenyl (diterpene) unit.¹⁶ Indole diterpenes identified in endophyte-infected perennial ryegrass are lolitrems A to E,^43,65 lolitriol,⁶⁶ and paxilline¹⁰⁵ (Figure 1). The lolitrems and paxilline are potent neurotoxins that cause sustained tremors when injected into, or fed to, mice or sheep,⁴² and both mycotoxins are toxic and deter feeding by the Argentine stem weevil.^77,85 Several other indole diterpene mycotoxins isolated from Aspergillus and Penicillium species also possess insecticidal activity^31,103 and such activity may be widespread among this class of metabolites. Endophytes that produce significant quantities of lolitrems, in their natural hosts, have appeared restricted in distribution to within perennial ryegrass and tall fescue ecotypes,^19,20,58 to F. longifolia infected with E. ty...

Table of contents

• Cover
• Title Page
• Copyright Page
• Table of Contents
• SECTION I: PRINCIPLES OF CLASSIFICATION AND TAXONOMIC GROUPS
• SECTION II: METHODS FOR CULTIVATING AND DETECTING GRASS/ENDOPHYTE INTERACTIONS
• SECTION III: ECOLOGY OF ENDOPHYTE-INFECTED GRASSES
• SECTION IV: CHEMICAL CONSTITUENTS AND TOXICITY
• SECTION V: BIOTECHNOLOGICAL USES OF ENDOPHYTES: GRASS IMPROVEMENT BASED ON MOLECULAR TECHNIQUES
• SECTION VI: UTILIZATION OF ENDOPHYTE-INFECTED GRASSES BASED ON AGRONOMIC CHARACTERISTICS
• Index