Population Genetics, Endosymbionts and Bunchy Top Virus Studies of Banana Aphid (Pentalonia sp.) in the Philippines

Galambao, Marciana Baja (2021) Population Genetics, Endosymbionts and Bunchy Top Virus Studies of Banana Aphid (Pentalonia sp.) in the Philippines. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Managing and controlling perennial plant diseases to increase agricultural production while protecting the environment is an important strategy in integrated pest management and sustainable agriculture. Using molecular ecology tools, I study the banana aphid (Pentalonia nigronervosa Coquerel), an insect vector which play an important role in the acquisition and spread of bunchy top disease caused by abaca bunchy top virus (ABTV) and banana bunchy top virus (BBTV) affecting abaca (Musa textilis Nee) plants across three abaca germplasm collections in the Leyte, Sorsogon and Davao regions of the Philippines. First, I study the reproductive mode, genetic diversity and population genetic structure of the banana aphid using microsatellite markers. I found that they reproduce asexually with low genetic diversity and that two Pentalonia species are infecting abaca plants in the Philippines. Second, I identify the infection, composition, and distribution of facultative bacterial endosymbionts in these two aphid species, determine if aphids hosted the same symbionts within aphid colony, and evaluate if they were influenced by geographic location, aphid species and the plants susceptibility to bunchy top disease. I found that four endosymbiotic bacteria infected Pentalonia aphids and infections were not consistent within aphid colony. Geographic location influenced endosymbiont communities but did not vary with aphid species and across abaca accessions. Lastly, I identify the bunchy top virus infecting banana aphid and quantify the viral load present in a single aphid. I found that BBTV was present and seemed to be causing bunchy top disease in abaca. I then determine the distribution of the virus across germplasm collections and evaluate if the presence or viral copy number was influenced by collection location, Pentalonia species, the endosymbionts present, whether ants were present on the plants the aphids were collected from and plant susceptibility to the disease. I found that the presence of BBTV depended on collection sites and aphid species, and that infection was highest in Davao but lowest in Sorsogon. Meanwhile in Leyte, I found that Pentalonia species and Wolbachia were observed as the main factors that influenced the presence of BBTV. With these findings on the population genetics, endosymbionts, and the bunchy top virus in banana aphids, I discuss the implications for bunchy top disease management on abaca and make recommendations for future sustainable integrated pest management strategies of abaca bunchy top virus in the Philippines