Show simple item record

dc.contributor.authorAbang, A.F.
dc.date.accessioned2022-06-20T13:04:04Z
dc.date.available2022-06-20T13:04:04Z
dc.date.issued2018
dc.identifier.citationAbang, A.F. (2018). Interactions between the germplasm of okra (Abelmoschus spp.) and Aphids with special reference to Aphis gossypii Glover (Hemiptera: Aphididae) in Cameroon. Yaounde, Cameroon: University of Yaounde 1 (202 p.).
dc.identifier.urihttps://hdl.handle.net/20.500.12478/7514
dc.description.abstractAphis gossypii Glover (Hemiptera: Aphididae) is one of the major pests of okra (Abelmoschus spp). On one hand, direct damages due to its feeding habit results in curling and deformation of young leaves. On the other hand, indirect damages are caused because of honeydew secreted on fruits and leaves with, which in turn may promot growth of black sooty mould. The black sooty mouls stain and reduce fruit and leaf quality and reduce photosynthetic activity. In addition, honeydew attracts ants that fend off natural enemies of Hemipterans. The severity of aphid infestation has led to widespread use of chemical pesticides for its control with adverse effect that it also eliminates the natural enemies. Pests including aphids such as A. gossypii are becoming resistant to pesticides. Most vegetable farmers in Cameroon accept that they use chemical pesticides, and are equally willing to accept new varieties that are resistant to pests and diseases, to minimize the use of pesticides. The objective of this work was to identify aphid-resistant okra germplasm for a better management of A. gossypii. Screening trials were conducted under natural field conditions without pesticide application. Aphid infestations per variety were directly scored on one leaf per stratum on three strata of five plants randomly selected. The number of aphids was recorded using the following scale: 0 = no aphids present; 1 = 1 to 10 aphids per leaf; 2 = 11 to 100 aphids per leaf; 3 = 101 to 500 aphids per leaf; and 4 = >500 aphids per leaf. Phenotypic structures and secondary metabolites that could affect the life traits of Aphis gossypii were analysed. In the case of phenotypic structures, trichome density, hardness and chlorophyll content of okra leaves were taken into consideration. Concerning secondary metabolites, leaf contents in total phenols, total tannins, free amino acides, total sugars, reducing sugars, total nitrogen and potassium were considered. The implications of mechanisms of tolerance, antibiosis and antixenosis were evaluated in the analysis of resistance of plants of Abelmoschus spp. Nine okra accessions were therefore identified as resistant or moderately resistant to A. gossypii. The most resistant ones were VI041210, VI057245 and Gombo caféier. The farmers’ check Kirikou and VI060694 were the most tolerant. Resistant accessions produced fewer pods than susceptible and tolerant accessions. In this study, non-preference (antixenosis) was not a category of resistance. The non-discrimination between susceptible and resistant accessions in aphid settling behaviour indicates that phenotypic structures and plant metabolites did not influence attraction and settling behaviour. The trichome density was highest on the leaves of the top stratum, higher at the middle stratum and lower at the bottom; it was lower on VI060794 and the farmers’ check, Kirikou, at all plant strata, and may favour infestation of these susceptible accessions. The current study revealed the role of total nitrogen content in leaves leading to the susceptibility of okra accessions to aphids. VI060794 that was the most susceptible in Taiwan in 2013 and in the second season of the confirmatory screening trial in Cameroon in 2014 had significantly higher leaf Nitrogen content than in other accessions. Constitutively, the role of free amino acids, tannins and total phenols in imparting resistance against A. gossypii in the identified okra accessions during our study is inconclusive. Biochemical studies of accessions of okra at 6 and 10 weeks after sowing showed that total phenols and tannins content changed following aphid infestation. Total tannins increased in the resistant accessions and reduced in Kirikou, the susceptible farmers’ check at all plant growth stages. The total sugars, potassium and reducing sugars played a role in offering resistance in plants with or without aphids. As a susceptible accession, VI060794 had higher nitrogen content significantly at vegetative stage following aphid infestation and at reproductive growth of plant even when plants were not infested. The farmers’ check Kirikou that was one of the most susceptible to aphids had the highest intrinsic rate of natural increase of aphid population, which was significantly different from that of VI057245, one of the most resistant accessions during confirmatory and multilocation trials. When plants were previously infested with aphids at vegetative and reproductive stages, the developmental time was significantly longer on VI041210 than on all accessions except VI060688 at vegetative growth. No mortality of aphids was observed on VI033805, VI033824 and on the farmer’s check Kirikou. Results from the multilocation trials indicated that the farmers’ varieties were more susceptible to aphids than most of the selected resistant accessions, across all agro-ecological zones. VI057245 and VI036213 are suitable for resistance to aphids in the western highland; VI060818, VI060794 and VI039614 in the monomodal humid rain forest; VI060794, VI057245, VI051114 and Gombo caféier for the bimodal humid rain forest, VI060818 and VI041210 in the Sudano-Sahelian region. VI060794 was also the most yielding in all ecozones in Cameroon and with some acceptable level of resistance. We recommend the following accessions for the presence of resistant traits: VI041210, VI051114, VI033824, VI057245 and VI036213 for leaf trichomes; VI051114 and VI036213 for fruit size; VI041210, VI060794 and Gombo cafiere for plant vigour. VI041210, VI057245 and Gombo cafiére for higher secondary metabolites and lower plant nutrients contents leading to antibiosis. VI060794 presents superior qualities in terms of yields and management of aphids. It will also be interesting to study the genotypes of the selected accessions to identify genes associated with resistance to A. gossypii.
dc.format.extent202 p.
dc.language.isoen
dc.publisherUniversity of Yaounde I
dc.subjectAphis Gossypii
dc.subjectOkras
dc.subjectAphids
dc.titleInteractions between the germplasm of okra (Abelmoschus spp.) and Aphids with special reference to Aphis gossypii Glover (Hemiptera: Aphididae) in Cameroon
dc.typeThesis
cg.contributor.affiliationUniversity of Yaoundé I
cg.contributor.affiliationInternational Institute of Tropical Agriculture
cg.coverage.regionAfrica
cg.coverage.regionCentral Africa
cg.coverage.countryCameroon
cg.coverage.hubCentral Africa Hub
cg.researchthemePlant Production and Health
cg.identifier.bibtexciteidABANG:2018
cg.authorship.typesCGIAR and developing country institute
cg.iitasubjectAgronomy
cg.iitasubjectFarming Systems
cg.iitasubjectPlant Diseases
cg.iitasubjectPlant Production
cg.notesIITA supervisor: Dr. Hanna, R.
cg.publicationplaceYaounde, Cameroon
cg.accessibilitystatusLimited Access
cg.reviewstatusInternal Review
cg.usagerightslicenseCopyrighted; all rights reserved
cg.targetaudienceScientists
cg.futureupdate.requiredNo
cg.contributor.acknowledgementsThis study was conducted with the financial support of the Federal Ministry for Economic Cooperation and Development, Germany (BMZ) and the German Society for International Cooperation (GIZ). I want to thank AVRDC-The World Vegetable Center for giving me this opportunity in this prestigious institution. I am grateful to the Director General, Pr. John Donough Heber 'Dyno' KEATINGE; the Deputy Director General for Research, Dr. Jacqueline HUGHES and the Deputy Director General for Administration and Services, Dr. Yin-fu CHANG, all from AVRDC-World Vegetable Center, for the training opportunity. The success of this research study has been achieved through the special supervision of Dr. Srinivasan RAMASAMMY who believed in me. He supported me not only professionally and scientifically, but also socially and morally. His advices and recommendations gave me the inspirations, motivations, and the undestanding I needed for a pleasant and fruitful research. I also thank my first academic supervisor, Pr. Sévilor KEKEUNOU, for setting the pace and guidance throughout the training. He has given my research work the quality it deserves. My profound gratitude goes to my second academic supervisor, Pr. Charles-Felix BILONG BILONG, who provided a solid academic backing to enable me meet the challenges of my research, both institutionally and professionally. His critics and amendments improved my knowledge and understanding, and I am grateful for the time he spent to make sure my thesis was up to standards. Dr. Rachid HANNA, the Principal Investigator of the project and Country Representative of IITA-Cameroon did all his best to fill all the gaps and loop holes to ensure the smooth running of my activities. I am grateful for his endless assistance and trust. This project was one of the key responsibilities of AVRDC’s Regional Director for West and Central Africa, Dr. Abdou TENKOUANO. I acknowledge the relevant contributions he made to improve credibility during the study. I want to thank Drs. Takemore CHAGAMOKA, Martin YEBOAH and Jean-Claude BIDOGEZA, who were successively my administrative supervisors as AVRDC’s Cameroon Liaison Officers, for the encouragement they gave me. This was based on the confidence they had in me, and their close observation and monitoring of my activities to guide me during my work. Dr. Christophe KOUAME, the first Liaison Officer for Cameroon has been like a guardian to me and I can never forget his contribution in helping me achieve my career objectives. I thank the entire staff of AVRDC Cameroon (Dr. Klaus FLEISSNER, Ms. Regine KAMGA, Mr. Njoh WANDUKU, Mr. Achu JOACHEM, Mr. Ronal CHENDJOU NZOUKOU, Ms. Sharon EKUE, Ms. Geraldine NJUMBE, Ms. Lyliane PONSSOU, Ms. Emily Ijang GAWUM, Ms. Viviane Nadège MBITA and Mr Gang Syril) and Taiwan (Ms. Mei-yin LIN, Mr. Fu-cheng SU, Ms. Grace HSU and Ms. Angela CHEN) for considering my research activities as part of their responsibilities. Dr. Greg LUTHER, Global Technology Dissemination Specialist and Ms. Lydia LU, Training Coordinator at AVRDC Taiwan and Dr. Jaw-Fen WANG, Pathologist and Global Leader for Theme Production ensured that I had a successful training as a scholar at AVRDC Cameroon as well as Taiwan. My training was also successful, thanks to Dr. Ray-Yu YANG, AVRDC‘s Nutritionist and the entire staff of the nutrition unit in Taiwan for welcoming me in the laboratory and assisting in providing protocols and in maniputing the equipements during studies and analysis of plant metabolites. With the help and talents from Dr. Jan CHANG, Scientist in Biotechnology, I was able to acquire knowledge in molecular entomology. Additional knowledge about okra was acquired thanks to Dr. Sanjeet KUMAR, AVRDC’s Pepper Breeder (earlier as an Okra Breeder in West Africa). His inputs that were scientifically important for this study are appreciated. I cannot forget to thank the staff of AVRDC’s refectory and the dormitory service led by Ms. Sylvia HSU for the meals and quality services that made my stay at AVRDC Taiwan comfortable. My parents, brothers and sisters were there for me and provided a comfortable home with stable and constant support materially and morally. My wife, Marcelline NKENGLACK ABANG has been the source of extra energy I needed to conquer all obstacles. Her assistance cannot be measured. My classmate, colleagues, friends and well-wishers were sources of encouragement. They provided a forum for exchange of ideas, assistance and support. I wish them success in their endeavours. Finally, the University of Yaoundé I my Alma mater remains a place where I own my respect and honour. I wish to thank the university authorities, lecturers and the supporting staff for my education.


Files in this item

Thumbnail

This item appears in the following Collection(s)

Show simple item record