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ARE Stemphylium Spp. SEED BORNE PATHOGENS of PEA (Pisum Sativum L.) I Chapter 1 General Introduction I Chapter 2 Literature Review

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ARE Stemphylium Spp. SEED BORNE PATHOGENS of PEA (Pisum Sativum L.) I Chapter 1 General Introduction I Chapter 2 Literature Review Lincoln University Digital Thesis Copyright Statement The digital copy of this thesis is protected by the Copyright Act 1994 (New Zealand). This thesis may be consulted by you, provided you comply with the provisions of the Act and the following conditions of use: you will use the copy only for the purposes of research or private study you will recognise the author's right to be identified as the author of the thesis and due acknowledgement will be made to the author where appropriate you will obtain the author's permission before publishing any material from the thesis. Are Stemphylium spp. Seed Borne Pathogens of Pea (Pisum sativum L.)? A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Horticultural Science At' Lincoln University , .. :' ' .. ' By I C.S.P. Teixeira Lincoln University 2005 I i iI ' ",' ;-. Abstract of a thesis submitted in partial fulfilment of the requirements for the Degree of M. Hort. Sc. Are StemphyUum spp. seed borne pathogens of pea (Pisum sativum L.) ? by C. S. P. Teixeira The effects of Stemphylium spp. on pea seeds and plants were studied in four controlled environment and laboratory experiments. Laboratory seed health testing of commercial pea seed lots established that Stemphylium spp. can be 1'-.--'<:':--, , seed borne in peas, with infection levels varying from 0 to 46% depending on i:' ,. ' --'. I'> production season and cultivar. Stemphylium spp. were isolated from naturally infected marrowfat pea seeds, grown on artificial culture media, and their characteristics described. Molecular tests performed by the Plant Pathology Laboratory, USDAIARS (USA), confirmed the five main species isolated were: S. loti Graham, S. vesicarium (Wallr) Simmons, S. herbarum Simmons, S. astragali Yoshii and S. sarciniforme (Cavara) Wiltshire. Stemphylium spp. did not kill seeds or affect laboratory seed germination. The species of Stemphylium isolated from seeds are likely to vary in their pathogenicity and ability to reduce viability. Of the isolates, an isolate of Stemphylium herbarum produced the most conidia. This isolate was tested in a third experiment in order to determine its pathogenicity on pea plants. Plants at three different stages of development were inoculated with sterile distilled water, sterile distilled water plus Tween, S. herbarum conidial suspension and S. herbarum conidial suspension plus ii Tween. Under the conditions (mean temperature of 19°C and lOO% relative humidity) S. herbarum caused lesions on pea leaves, especially in the early stages of plant development (seedlings at the 3- 5 node stage). Symptoms observed were brown, irregular to oval shaped lesions, approximately 6mm in diameter. On a scale of 0-5 seedlings inoculated with conidial suspension of the fungus had a mean disease score of 2 while untreated plants had a disease score of O. The mean leaf diseased tissue area was also higher for seedlings inoculated with S. herbarum conidial suspension than for untreated seedlings 2 2 (29 mm cf. 0 mm , respectively). Scanning electron microscopy revealed that S. herbarum penetrated the leaf tissue via the epidermis as well as the stomata. Infection was more successful on seedlings than adult plants. Stemphylium herbarum was re-isolated from infected tissue, thus fulfilling Koch's Postulates. Movement of the fungus from infected leaf tissue to seeds was not demonstrated. Infected seeds may be the first source of inoculum of Stemphylium spp., ensuring the perpetuation of the fungi and their spread to new areas. Experiment four tested the effectiveness of registered seed treatments for peas (Aliette super, Apron XL and Wakil XL) and a hot water soak treatment (50 ± 0.5°C for 30 minutes) for control of Stemphylium spp. Chemicals had limited success in controlling Stemphylium spp. infection. Hot water treatment was the most effective method, eliminating lOO% of Stemphylium spp. from the seed lots tested, but it was harmful to the seeds, reducing germination by approximately 34 %. i ! Keywords: Stemphylium, seed, peas, seed borne, pathogenicity, seed treatment. iii Contents Page Abstract........................................................................................................... 11 Contents .......................................................................................................... IV Tables .............................................................................................................. IX Figures ............................................................................................................ Xl1 List of Appendices......................................................................................... xvi 1 General introduction ............................................................................... 1 1.1 Overview ................................................................................................... 1 1.2 Objectives .................................................................................................. 4 1.3 Thesis structure ......................................................................................... 5 2 Literature review ..................................................................................... 7 2.1 Peas ............................................................................................................ 7 2.1.1 Pea origin and distribution ..................................................................... 7 2.1.2 Pea Production ....................................................................................... 7 2.1.3 Pea Systematic ....................................................................................... 8 2.1.4 Morphology ............................................................................................ 8 2.1.4.1 Vegetative development ...................................................................... 8 2.1.4.2 Reproductive Development.. ............................................................... 9 2.1.5 Pea seed development .......................................................................... 10 2.1.6 Seed structure ....................................................................................... 12 2.1.7 Pea types ............................................................................................... 12 2.1.7.1 Classification according to growth habit .......................................... 12 2.1. 7.2 Classification according to the purpose of use ................................. 13 2.1.7.3 Marrowfat Peas ............... :................................................................. 13 2.1.8 Production of marrowfat peas in New Zealand ................................... 14 2.1.9 Pea crop establishment and management ............................................ 15 2.2 Diseases of peas ...................................................................................... 17 2.2.1 Diseases caused by fungi ..................................................................... 17 2.2.2 Diseases caused by bacteria ................................................................. 23 2.2.3 Diseases caused by viruses .................................................................. 24 2.2.4 Pathogenicity ........................................................................................ 25 2.2.5 Stemphylium spp. and peas .................................................................. 26 2.3 The genus Stemphylium ........................................................................... 27 2.3.1 Symptoms caused by Stemphylium spp. in forage legume crops ........ 28 iv 2.3.1.1 Lucerne and clover ............................................................................ 28 2.3.1.2 Chinese milk vetch (Astragalus sinicus L.) ...................................... 29 2.3.2 Vegetable crops .................................................................................... 29 2.3.3 Spinach and asparagus ......................................................................... 29 2.3.3.1 Onion (Allium cepa L.) and Garlic (Allium sativum L.) ................... 30 2.3.3.2 Solanaceae crops ............................................................................... 30 2.3.3.3 Lettuce (Lactuca sativa) .................................................................... 31 2.3.3.4 Pears .................................................................................................. 31 2.3.4 The life cycle and environmental requirements for Stemphylium spp. 31 2.3.5 Effects of Stemphylium spp. on crop yield ........................................... 33 2.3.6 Phytotoxins produced by Stemphylium spp. and pathogenicity ........... 34 2.3.7 Stemphylium spp. in New Zealand ....................................................... 35 2.3.7.1 Disease assessment. ........................................................................... 36 2.3.8 Stemphylium spp. in pure culture (isolation, incubation, identification) ................................................................................... 37 2.3.8.1 Conidial morphology ........................................................................ 38 2.3.9 Phylogeny of Stemphylium spp ............................................................ 40 2.4 Seed borne plant diseases ........................................................................ 43 2.4.1 Seed infection mechanisms .................................................................. 45 2.4.2 Seed health testing ...............................................................................
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