Field and Postharvest Biology of Dendritic Spot and Stem End Rot of Mango
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Field and Postharvest Biology of Dendritic Spot and Stem End Rot of Mango Arslan Jabeen B.Sc. (Hons.) (University of Arid Agriculture, Rawalpindi, Pakistan) M.Sc. (Hons.) (PMAS-Arid Agriculture University, Rawalpindi, Pakistan) A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2016 School of Agriculture and Food Science Abstract Stem end rot is a well-established postharvest disease of mango caused by the fungi Neofusicoccum parvum (Pennycook & Samuels) Crous, Slippers and A.J.L. Phillips and Lasiodiplodia theobromae (Pat.) Griff & Maubl. Dendritic spot is a newly emerging disease of mango. The pathogenic fungi which cause anthracnose and stem end rot such as Colletotrichum gloeosporioides (Penz.) Penz & Sacc. in Penz and N. parvum respectively also cause dendritic spot of mango. However, a number of other fungi such as Fusicoccum sp., Alternaria sp. and Lasiodiplodia theobromae have also been isolated from dendritic spot symptoms from time to time. Very little work has been reported on dendritic spot as the symptoms of this disease are easily confused with other skin blemishes of mango such as tear stain. This study investigates the aetiology of dendritic spot. Fruit bagging experiments were carried out on Kensington Pride (KP) and R2E2 cultivars of mango to investigate the time of infection of dendritic spot and stem end rot. The fruit were bagged at four different growth stages. The results showed that fruit bagged at golf ball size which remained bagged until harvest had low incidence of dendritic spot and stem end rot. Higher incidence was observed in the fruit which were bagged close to harvest and the un- bagged control fruit. It was concluded from the results that pathogens invade the fruit at an early growth stage and fruit protection at this stage of growth can help in minimizing postharvest disease incidence. The effect of conventional and improved orchard practices on the management of anthracnose and stem end rot was also studied. The experiment was carried out in Pakistan. Three districts of Punjab province of Pakistan were selected for the study. The fruit of Chaunsa cultivar of mango were collected from growers‟ conventional practice blocks and ASLP (Agriculture Sector Linkages Program) improved practice blocks. In the conventional practice blocks, there was irregular application of foliar and pesticides sprays, non-consistent use of fertilizers with a minimum use of cultural practices such as irrigation, pruning, weeding and soil nutrition analysis, use of recommended foliar sprays of fungicides for disease management at different fruit growth stages, pest management and nutrient management by annual application of NPK. Whereas, the improved practice blocks were maintained by cultural practices. A low incidence of anthracnose and stem end rot was observed in the fruit which was collected from the ASLP improved practice blocks as ii compared to the incidence observed in the fruit collected from the conventional practices blocks. Postharvest application of exogenous ethylene on mature fruit to induce uniform skin colour and ripening and hot fungicide dips to minimize postharvest disease incidence are common practices used by Australian mango growers. Early fruit ripening facilitated by exogenous ethylene is helpful in early fruit marketability, but it can result in higher disease incidence in case of prolonged fruit storage or higher fruit storage temperature. The effect of exogenous ethylene and hot fungicide dip with fludioxonil was investigated when both treatments were applied on the fruit alone and in combination with each other. The results showed that the application of exogenous ethylene alone caused higher incidence of dendritic spot and stem end rot when the fruit received frequent rainfall during the growing season. This higher incidence of both dendritic spot and stem end rot could also be because of accelerated fruit ripening and decline in fruit resistance. But, when low or no rainfall was received during the season, a low incidence of dendritic spot and stem end rot was observed when the exogenous ethylene was applied on the mature fruit. Fruit hot-dipped in the fungicide fludioxonil followed by the exogenous ethylene had zero to minimum incidence of both dendritic spot and stem end rot. Market surveys were carried out to determine the geographical distribution of the dendritic spot pathogens and to collect the dendritic spot and stem end rot pathogens. Disease pathogens were isolated from fruit from Northern Territory, North and Southeast Queensland. All isolates of Colletotrichum collected from anthracnose were identified morphologically and phylogenetically as C. gloeosporioides but the isolates which were collected from the dendritic spot symptoms were identified by Internal Transcribed Spacer (ITS) and Trans elongation Factor (TEF) 1- α as, C. gloeosporioides, C. siamense, and C. asianum. All the Neofusicoccum isolates collected from dendritic spot and stem end rot symptoms were identified as N. parvum and N. occulatum by using the ITS and TEF gene regions. One isolate of stem end rot was identified as Botryosphaeria dothidea. To determine the role of C. gloeosporioides, N. parvum, L. theobromae and Alternaria sp. in causing dendritic spot in mango, the isolates of these fungi were assessed for pathogenicity. This work identified C. siamense, C. asianum, N. parvum and N. occulatum as the most virulent pathogens causing dendritic spot. Keywords: Dendritic spot, stem end rot, field biology, pre and postharvest treatments. iii Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis. iv Publications during candidature Conference abstracts Arslan Qureshi, Victor Galea, Chrys Akem, Elizabeth Aitken, Ian Bally, 2013. The effect of postharvest hot fungicidal dip and exogenous ethylene gas application on the incidence of dendritic spot and stem end rot in Kensington Pride (KP) mangoes. The 19th Australasian Plant Pathology Conference, 25 – 28 November, 2013, Auckland, New Zealand. Arslan Qureshi, Victor Galea, Chrys Akem, Elizabeth Aitken, Ian Bally, 2013. The effect of bagging on the incidence of dendritic spot and stem end rot in Kensington Pride and R2E2 varieties of mango. The 19th Australasian Plant Pathology Conference, 25 – 28 November, 2013, Auckland, New Zealand. Industry Publications Qureshi AJ (2011). Dendritic spot and stem end rot. Mango Matters spring/ summer: pp. 9 (AMIA & HAL publishing). Publications included in this thesis No publications included. Contributions by others to the thesis No contributions by others. Statement of parts of the thesis submitted to qualify for the award of another degree None. v Acknowledgements All praises for Almighty Allah (SAW) for His guidance and countless blessings upon me to succeed all the challenges in my life. I would like to say a very special thanks to my principal adviser Associate Professor Dr Victor J. Galea for his invaluable guidance, knowledge, healthy criticism and fatherly behaviour for me. I cannot express my gratitude for him in words. I also thank to my co-adviser Dr Chrys N. Akem for his support during my research, his encouragement and above all for his presence whenever I needed. Very special thanks to my co- advisers Project leader ASLP mango project Senior Horticulturist Dr Ian S.E. Bally and Associate Professor Dr Elizabeth A.B. Aitken for their continuous guidance support and constructive advises to improve my writing skills. My sincere thanks to my milestones examiners Professor Peer Schenk and Senior Lecturer Dr Doug George for their valuable advice about my research project. Special thanks to Dr Lindy Coates, Senior Plant Pathologist, Plant Pathology Group, DAF, Eco Sciences Precinct, Brisbane and her team for their help during my research, a very constructive feedback on some chapters of my thesis and also for providing me the opportunity to work with them to improve my research skills. I gratefully thank to Mr Rowland Holmes for helping me in accessing the farmer orchards for fruit collection and for arranging the hot fungicidal dips and exogenous gas applications of fruit at commercial facilities. A special thanks to Dr Ken Goulter and Associate Professor Jennifer Seddon for their kind advice, support and guidance during the phylogenetic studies and sequence analysis of the pathogens. I thank to Mr Victor Robertson for his technical assistance. Thanks to Mr Allan Lisle (SAFS bio- statistician) for his guidance and support during statistical analysis. Thanks to the farmers for their generous offer of using the fruit for research purposes and for assistance in postharvest fruit treatments.