ADAPTATION OF ANDEAN DRY BEAN (Phaseolus vulgaris L.) GENOTYPES TO DROUGHT STRESS

Transcription

1 ADAPTATION OF ANDEAN DRY BEAN (Phaseolus vulgaris L.) GENOTYPES TO DROUGHT STRESS By Kabutbei Jepngetich B.Sc. Agric. (Hons), University of Nairobi A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF THE DEGREE OF MASTER OF SCIENCE IN AGRONOMY DEPARTMENT OF PLANT SCIENCE AND CROP PROTECTION, FACULTY OF AGRICUTURE UNIVERSITY OF NAIROBI 2014

2 DECLARATION I declare that this is my original work an&has not been presented for any award of a degree any other university Signature... r &, Date \3\^W^. Kabutbei Jepngetich. This thesis is submitted with our approval as supervisors: si,,,,, QSli na, [^\%\M!.^... ' Prof. George N. Chemining'wa Department of Plant Science and Crop Protection University of N S ignature^-#l/! Z.f...'.. T...~.T..' Date. Prof. Paul M. Kimani Department of Plant Science and Crop Protection University of Nairobi. Signature. Prof. Mary W.K Mburu South Eastern Kenya Univ Date Signature. Date. Prof. John H. Nderitu Department of Plant Science and Crop Protection, University of Nairobi.

3 GENERAL ABSTRACT Common bean (Phaseolus vulgaris L.) is the principal food legume in eastern Africa. However, most of the large seeded varieties grown by farmers are susceptible to drought. Adaptation to drought stress is therefore an increasingly important trait in Andean dry beans due to climate change and variability which has resulted to a reduction in water resources, a shift in production areas, frequent crop failure and food insecurity, and emerging strong market preferences in Africa. Little work has been done to develop drought tolerant large seeded bean varieties in eastern Africa. As a result drought tolerance of large seeded commercial cultivars and breeding lines is not well understood. Development, identification and dissemination of drought tolerant varieties is an important strategy to reduce the chances of crop failure and improve food security in this region. Therefore, the objectives of the study were to involve farmers in selection of drought tolerant Andean bean varieties and to determine the agronomic performance and genotypic variation in physiological traits of Andean bean genotypes under drought stress. Seventy-three advanced large seeded bean lines and 15 check cultivars were evaluated under drought stress and reduced stress conditions in farmer participatory trials conducted at Kabete and Mwea (Kirinyaga South District) during the 2011 short rains season and 2012 long rain seasons. The trial was laid out in a randomized complete block design with a split plot arrangement with two replicates. Drought stress was imposed at pre-flowering stage. Data on agronomic performance and physiological traits were taken during plant growth under both reduced and drought stress. At maturity stages, farmers were involved in selection of drought tolerant Andean varieties following the ribbon method at Mwea and Kabete. The results showed that farmers' key selection criteria included plant architecture, earliness, crop uniformity, pod clearance, yield and yield components, seed traits and grain marketability, and post harvest utilization. The outstanding desired traits for a preferred variety were high yields, drought tolerance, determinate growth habit, attractive vii

4 grain colour, earliness, resistance to pests and diseases, uniformity of maturity, good ground clearance, vigorous growth and good taste when cooked. The genotypes that were most preferred and identified to have farmer and consumer preferred traits included DRM 11-17, DRM 11-13, DRM 11-18, DRK 11-15, DRK 11-18,' DRK 11-16, DRK 11-17, DPC 11-06, DPC 11-08, DPC 11-09, DSS 11-01, DSS 11-08, DSS and DSS The results also showed gender differences in the selection criteria. Men preferred high yielding varieties irrespective of grain colour while women preferred varieties with red grains. Men also rejected climbing varieties as unsuitable when intercropped with maize and preferred varieties with high shoot biomass for fodder. These differences emphasized the need to involve both men and women in participatory variety selection. Genotypes that were identified to be among the most tolerant to drought included, DRK 11-05, DRK 11-10, DRK 11-16, DRK 11-18, DRM 11-03, DRM 11-13, DRM 11-17, DSS 11-01, DSS 11-04, DSS 11-16, and DSS 11-17, which had mean yield advantages over the local drought resistant checks of 85, 68.7, 43.9, 51.8, 20, 41.9, 48.6, 57.5, 105.9, 75.5 and 101.8%, respectively, under drought stress. Participatory variety selection showed that 62% of these drought tolerant genotypes had farmer and consumer preferred traits. These genotypes exhibited accelerated phenological development. The genotypes also demonstrated resistance to intermediate resistance to diseases; angular leaf spot, leaf rust, floury leaf spot and bean common mosaic virus. Genotypic differences were noted in grain yield, pods per plant, seeds per pod and 100-seed weight under both drought stress and reduced stress. The genotypes identified as drought tolerant had consistently higher values of grain yield and yield components. Results also showed that genotypes DRM 11-03, DRM 11-17, DRK 11-18, DSS and DRK were efficient in photo-assimilate remobilization as they had higher values of harvest index, pod harvest index, pod partitioning index and lower values of pod wall biomass proportion. Genetic variation was found in the partitioning indices; pod harvest viii

5 index, pod wall biomass proportion and harvest index. Some genotypes had lowered leaf temperature (temperature depression), to prevent excess loss of water through transpiration. The genotypes that showed this mechanism included DRM 11-17, DRK and DRK which had a difference of less than 3 C under the two stress levels. Chlorophyll content was found to be genetically controlled as it varied with genotypes. Environmental effect was also significant for this trait. The study resulted to the identification of new Andean bean genotypes with farmer and consumer preferred traits as well as more drought tolerant than the currently recommended varieties such as KAT 56, KAT 69, GLP 1004 and GLP 24. These genotypes could be used to widen the varieties that farmers can adopt to combat the effects of drought. They can also be used as sources of genetic resources for further breeding work and bean crop improvement. ix