SEASON OF HARVEST OF AmarAnthus cruentus L. IN RELATION TO SEED-BORNE MYCOFLORA AND MAJOR SHOOT DISEASES BY AFOLABI ADEBANJO B.Sc. Hons (Lagos, 1976), M.Phil. (Ife, 1981) A Thesis in the Department oF AGRICULTURAL BIOLOGY' Submitted to the Faculty oF AgriCulture and Forestry In partial fulfilment oF the rEquiremEnts for the degree of UNIVERSITYDOCTOR OF OFPHILOSOPH IBADANY LIBRARY oF the UNIVERSITY OF IBADAN IBADAN April, 1990 - ii - ABSTRACT The quality of Amaranthus cruentus L. seeds were influenced both by seasons of harvest and varietal type. The wetness that accompanied harvests of the first (April- June) and second (August-October) seasons greatly-reduced the quality of seeds of cultivars. Quality reduction were in the form of seed malformation,-dlscolouratlon and mycelial growth on them. Fifteen fungal species were founa to be associated with seeds~of the cultivars used. There was a seasonal variability in the occurrence, distribution and the quantity of the seed-borne fungi. Least number a nd mean percentage seed infec tion were r-eco r-de d for NHAC10-0 while NHAC30 and NHAc33 carried the highest per- centage inoculum on t he seed testa.. Thre~~ of the seed-borne fungi were highly pathogenic on seedlings of two of the cultivars wh Ile two of the fungi were seed transmitted. Six of these seed-borne mycoflora are new records on Amaranthus seeds in Nigeria. UNIVERSITY OF IBADAN LIBRARY For the two year trials, significantly (p=0.05) least incidence (0%) of dieback, stem blight (8%) were recorded during the first season for NHAc and NHAc while 4% mean 33 30 leaf blight was obtained from NHAc in the third (December-. 100 February) season. Least mean percentage leaf blight was · ~. -, _. iii. - recorded for all the cultivars also by the third season. Conversely, the second season recorded the highest incidence of all these aerial symptoms of the disease caused by Choanephora cucurbitarum (Berk & Rav.) Thaxt. in all the cu ltivars. Hot water treatment of infected seeds of all cultivars at 600C for 6 to 8 minutes completely disinfested them of the seed-borne funyi with consequent increase (7 95%) in seedling emergence. Also soaking in or dusting of infected see ds with a mixture of Benlate-Captafol or single Captafol at lag a~i./kg seed controlled the seed-borne fungi. Pre- harvest sprays of BenLet.e=Capt af oI mixture or Captafol at 3.3 kg/ha controlled inflorescence infection and seed-borne fungi with resultant yield increases and seedling emergence 'over the non-treated con trol. UNIVERSITY OF IBADAN LIBRARY ',,' '" ~ !~" .: 1 '. '.' - iv - ACKNOWLEDGEMENT I thank my supervisors Professor M.O. Adeniji and Dr. Tunde lkotun most sincerely for their good dispositions, ex pert Lse adv Lc e and very highly useful technical suggestions. Their wealth of experience made tremendous impact on the standard of this work. The experts on my Supervisory Committee: Drs. E.J.A. Ekpo, G.l. Atiri and A.O. Oladiran did a very thorough job. Their individual and collective suggestions, objective criticisms right from the proposal stage till the final write-up had helped a-lot in raising the stende rd of this work. They, also along with my supervisors assisted in reading through all stages of the work in good time on any of the occasions. I appreciate their input and express my profound gratitude to them all. I am grateful to the Ogun state University, A~go-Iwoye, Nigeria, for financial support during the course of this programme. The ManagUNIVERSITYement of the OFNation IBADANal Horticultural LIBRARYResearch Institute (NIHORT), Ibadan, Nigeria, assisted by allowing the use of their field, nursery and screen-house spaces. For this, I am indeed grateful. The assistance in statistical analysis rendered by .: : - v - Dr. Kunle Ogunfidodo (and his staff) of NIHORT and the computer facilities provided by the International Institute of Tropical Agriculture, IITA, are acknowledged with thanks. I also thank Mr. M.A. Shittu of NIHORT for handling the typing of this work at every stage. I thank my colleagues at the Department of Biological Sciences of the Ogun State University, Ago-Iwoye most sincerely and the Ajayis, Adebanjos of Oru Ijebu, Dosumus and others for sharing with me and soothing the anxiety experienced d urLn q this programme. Thanks to the International Mycological Institute, 1MI, of the C.A.B., Kew , for the identification and confirmation of fungi isolated from the seeds. 1 am also grateful to mother, Chief (Mrs.) S. Nuga- Adebanjo and my brother Mr. A.O. Adebanjo for my upbringing and encouragement. My devoted wife Adenike Oluwafunmilayo Adebanjo and all my children encouraged and supported me in all ways wh LLe on UNIVERSITYthis programme. OFI am IBADANindeed eve LIBRARYr grateful to them. - vi - DEDICATION This th~sis 1s affectionately dedicated to my eldiest sister Mrs. Esther Adedoja Onafeko (Nee Adebanjo) who thought it fit to send me to school at a very tender age despite the fact that we lost our fathe~ at a very tender age. UNIVERSITY OF IBADAN LIBRARY "j.' - vii - f12B11Y ICA TI0 N This is to certify that this work ncw submitted as a thesis for the degre·e of DOCTOR OF PHILOSOPHY of the University of Ibadan, is the result of investigations (except where reference is made to published literature and where assistance is acknowledged) by MR. AFOLAI3I ADEBANJO of the Department of Agricultural Biology, of the University of Ibadan, Nigeria and has not been part of any presentation for any other qualification. ' ===-::..-:=-:=::> ----------~ --'----~----------'- Acting Supervisor Dr. Tunde Ikotun B.Sc. (Hans.) Ibadan; Ph.D. (Land.); D.I.C., M.I. BioI. Department of Agricultural Biology UNIVERSITYUniversity OFof IbadaIBADANn LIBRARY Ibadan, Nigeria. - viii - TABLE:.....CONTENT2.E.- S Page TITLE ............................................... 1 ABSTRACT ............................................ il ACKNOWLEDGEMENTS .................................... iv DE;DlCATION •••• 41...................................... vi CERTIFICATION ..' .......~............................. vii TABLE OF CONTENTS ••••• fl ••••••••••••••••••••••••••••• viii LIST OF PLATES II • • • • • • • '. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Xi LIST OF FIGURES .......~...~......................... xii LIST or TABLES ,. ............. ......................... xiii CHAPTER 1 INTRODUCTION l~ • • • ., • • • • • • • • • • • • • • • • • • • • • • • • • 1 CHAPTER 2 LITERATURE REVIEW ......................... 5 2.1 Fungi infecting gRowing AmaranthuS PLaNTS 5 2.2 Seed-borne pathogens •••••••••••••••••••••• 7 2.3 Effect of seasons of harveST ON Seed-borne mycoflora ••••••••••••••••••••••••••••••••• 9 2.4 Control Of fieLd acquiRed ~Nd seed-borne pathogens ••••••••••••••••••••••••••••••••• 10 2.4.1 Seed treatments ••••••••••••••••••••••••••• 10 2.4.2 Pre-harvest chemical treatmenT ............ 14 UNIVERSITY OF IBADAN LIBRARY CHAPTER 3 MATERIALS AND METHODS ••••••••••••••••••••• 16 3.1 Seed source ••••••••••••••••••••••••••••••• 16 3.2 DeTectiON of MYcofLoral infecTion of seeds at seasons of harvest ••••••••••••••••••••• 16 3.2.1 Dry inSPection Method ••••••••••••••••••••• 18 3.2.2 Incubation methods •••••••••••••••••••••••• 18 (i) Blotter method •••••••••••••••••••••• 18 ( Ii) Agar plate MeThod ••••••••••••••••••• 20 - ix - page (a) preparation of culture medium ••••••••••• 20 3.2.3 Pathogenicity test of seed-borne fungi on seedlings ••••••••••••••••••••••••••••••• 21 3.2.4 Plating component parts of the seeds ••••••• 23 3.2.5 Seed transmission test ••••••••••••••••••••• 23 3.2.6 Investigating the effect of season of harvest on the incidence of shoot infections 25 3.2.7 Isolation of the pathogen from shoot tip, stem and leaf •••••••••••••••••••••••••••••• 25 3.2.8 Pathogenicity tests •••••••••••••••••••••••• 26 3.3 Control of seed-borne fungi by hot water treatment •••••••••••••••••••••••••••••••••• 28 3.4 Control of seed-borne fungi by chemical treatment •••••••••••••••••••••••••••••••••• 28 3.5 Control of inflorescence infection and field acquired mycoflora of seeds by pre-harvest spray of chemicals......................... 30 (i) Control of inflorescence infection 30 Effect of chemical application on seed yield •••••••••••••••••••••••••• 32 (i i:U Chemical control of seed-borne mycoflora and seedling emergence •••• 32 CHAPTER 4 REStJLTS ••.•••••••••••••••••••••••••••••••••••• 34 4.1 Dett~etion of my<!ofLoza I infac tion of seeds harves ted a'~ different seasons ••••••••••••• 34 4.1.1 Dry inspection method •••••••••••••••••••••• 34 4.1.2 IncubationUNIVERSITYmethod OF••••••• IBADAN••••••••••••••••••• LIBRARY 37 4.1.3 Pathogenicity test of seed-borne fungi on seedlings •••••••••••••••••••••••••••••••••• 42 4.1.4 Plating component parts of the seed •••••••• 51 4.1.5 Seed transmission test ••••••••••••••••••••• 55 4.2 Effect of season of harvest on the incidence of shoot infections •••••••••••••• 57 4.2.1 Isolntton of pathogen f~om diseased plant parts •••••••••••••••••••••••••••••••••••••• S9 - x - page 4.2.2 Pathogenicity tests of fungus on seedlings •••••••••••••••••••••••••••••• 61 4.2.3 Control of seed-borne fungi by hot water t r ea bme nt; •••••••••••••••••••••••••••••• 61 4.2.4 Control of seed-borne fungi by chemical treatment •••••••••••••••••••••••••••••• 68 4.2.5 Control of inflorescence infection and field acquired mycoflora of seeds by pre-harvest spray of chemicals ••••••••• 76 (1) Control of inflorescence infection ••••••••••••••••••••••• 76 (ii) Effect of chemical application on seed yield ••••••••••••••••••• 82 (iii) Chemical control of seed-borne