| dc.description.abstract | Soybean (Glycine max (L.) Merrill.) is a highly nutritious plant which plays an important role
in the world’s economy, however soybean rust disease caused by the fungus Phakopsora
pachyrhizi, is a major challange to the soybean industry. The disease among other constraints
has significatly affected crop yields in most soybean growing countries. High yield losses
associated with P.pachyrhizi, have been reported worldwide. The first report of the pathogen
in Kenya was made in 1996 and it has continued spreading agrressively and affecting soybean
bean industry in the country. Studies to determine resistance of soybean to rust disease have
only been done on commercial varieties but no such studies have been done on the local
varieties of soybean. Similarly no significant data has been collected on soybean rust disease
severity and incidence in the country. In this study, farmers’ participatory research was used
to collect data on soybean varieties preferred by farmers and the major constraint facing
soybean farming in Western Kenya region. Soybean rust disease incidence and severity levels
were also established in Khwisero, Butere, Mumias and Teso sub counties of Western Kenya.
The presence of the rust fungi was confirmed through microscopy and polymerase chain
reaction (PCR) analysis. Seven local varieties of soybean (Nyala, Bossier, SB19, Hill, SB8,
Gazelle and TGx1987-32F) were tested in the green house for resistance to soybean rust. To
determine presence of rust resistance genes, 12 Simple sequence repeat (SSR) markers
previously mapped on linkage groups of soybean were chosen and tested on the resistant
varieties. The study revealed that the farmers in Western Kenya region grow mainly the local
varieties of soybean and the area under soybean cultivation is <30% of the total land available
for crop production. It was further noted that soybean rust disease is present in all the subcounties
with the percent disease index (PDI) ranging from 40.37% to 74.8%. The disease
severity level in all the four sub-counties did not vary significantly (P<0.05). The disease
incidences per farm ranged from 22%-87% with Teso Sub-county recording the highest
average disease incidence (50.55%). Microscopy and PCR analysis identified the pathogen
causing soybean rust disease as P. pachyrhizi and not P. meibomiae. Screening for rust
resistance in the green house showed that the varieties TGx1987- 32F and SB8 were resistant
producing Red brown lesion with low level of severity, low lesion number, low sporulation
level and low area under disease progress curve (AUDPC) value. The other five varieties;
Nyala, Bossier, SB19, Hill and Gazelle were susceptible to rust producing Tan lesion with
profuse sporulation and high disease severity level. Simple Sequence repeats (SSR) markers
analysis of the resistant varieties showed that they both contained Rpp1, Rpp2, Rpp3 and Rpp4
genes while the susceptible varieties Rpp1, Rpp2 and Rpp4 genes. The results of this study
clearly indicate that adequate preventive measures have not been put in place to deal with
soybean rust disease and other constraints of soybean production. It has also been
demonstrated that the local varieties contain the rust resistance genes, however the resistance
can be overcome by certain rust pathotypes. The varieties that have shown resistance to
diverse rust isolates are possible sources of rust resistance genes that could be used in
breeding programs. | en_US |
