..JPG "Soybean leaves with Red brown lesions (TGx1987-32F).")
H.A. Ogot, S.A. Okoth,
G.O. Obiero, and J.M. Mahasi, from the different institute
of Kenya. wrote a Research article about, Defending Soybean: Screening Kenyan
Varieties Against Rust Disease. Entitled, Screening of selected kenyan soybean
varieties for resistance to Phakopsora pachyrhizi (Soybean rust). This research
paper published by the International Journal of Biosciences | IJB. an open
access scholarly research journal on Biosciences. under the affiliation of
the International Network For Natural Sciences| INNSpub. an open
access multidisciplinary research journal publisher.
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. In this study Seven varieties of soybean (Nyala,
Bossier, SB19, Hill, SB8, Gazelle and TGx1987-32F) commoly grown by
farmers in Kenya were tested in the green house for resistance to soybean
rust. The varieties TGx1987- 32F and SB8 showed resistant
reactions characterized by red brown lesion with low level of
disease 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 showed susceptible
reactions to soybean rust producing tan lesion with profuse sporulation
and high disease severity level. The Soybean varieties with low lesion
densities, low disease severity and low sporulation level may be possible
sources of rust resistance genes that can be used in breeding programs to
produce rust resistant varieties.
Read more : Nitrogen Choices Matter: Boosting Sunflower Oil Content in Morogoro | InformativeBD
Introduction
The production of
soybean in Kenya is affected by numerous biotic and abiotic factors. Some of
the constraints include, low yielding varieties, lack of markets, poor
agronomic practices, lack of awareness for its potential, competition with
other legumes, drought, water logging, and pest and disease attacks (Hartman et
al., 2011). Other factors include lack of varieties which are tolerant
midseason moisture stress and high yielding varieties tolerant to low
phosphorus (FAO, 2005). Among the biotic factors affecting soybean production
diseases are of great concern because of their final impact on yield. There are
a number of diseases that infect soybean worldwide the most common disease are
Anthracnose, bacterial blight, bacterial pustule, soybean rust, bean pod mottle
virus, brown stem rot, charcoal rot , frog eye leaf spot, soybean cyst nematode
and soybean mosaic virus among others (Ploper,1997).
Soybean rust caused
Phakopsora pachyrhizi as been identified among other diseases as the major
challenge to soybean production worldwide. Phakopsora pachyrhizi belongs to the
fungal phylum Basidiomycota, class Urediniomycetes and order Uredinales, which
produce uredinia, on “dome-like” structures that give rise to asexual
urediniospores. Hair-like hyaline hyphae called paraphyses grow inside
uredinia. Paraphyses and sporophores are base structures for urediniosopore
production (Bromfield, 1984). P. meibomiae is less aggressive while P.
pachyrhizi is more aggressive and infects over 95 species of plants from more
than 42 genera, including soybean and related Glycine species (Bromfield,
1984). The most susceptible host of P. pachyrhizi is kudzu (Pueraria lobata
(Wild.) Ohwi), a weed species that is commonly found in the United States of
America. Other common hosts are medic (Medicago arborea L.), lupine (Lupinus
hirsutus L.), sweet clover (Melilotus officinalis (L.) Lam), vetch (Vicia
dasycarpa Ten), common beans (Phaseolus vulgaris L.), lima and butter beans
(Phaseolus lunatus L.), pigeonpea (Cajanus cajan (L.) Millsp), garden peas
(Pisum sativum L.) and cowpeas (Vigna unguiculata) (Bromfield, 1984). Soybean
rust infection process begins in the low to mid-canopy and moves up the plant.
The infection process starts with urediniospores germination to produce a
single germ tube that grows across the leaf surface, until an appressorium is
formed. Penetration of epidermal cells is direct through the cuticle by an
appressorial peg (Miles et al., 2005). During the infection process
intracellular invasion of the leaf occurs once hyphae are formed within the
mesophyll layer. Within 5 to 7 days volcano shaped uredinia with round ostioles
are produced which release urediniospores on the abaxial surface completing the
asexual reproduction cycle (Goellner et al., 2010).
The rapid spread of the
disease in the continent of Africa has led to major decline in soybean yield
(Levy, 2005, Oloka et al., 2008). Losses due to soybean rust can be
significantly high. In South Africa losses of 10- 80% have been reported and in
areas under monocropping system the losses can be as high as 100%. India has
experienced losses of 10-90%, Japan 40% and Taiwan has reported losses of
23-90% in (Hartman et al., 1999). It is therefore important that the major
production constraints be addressed so as to improve the crop yield to be able
to meet the market demands and sustain the production industries. To control
the spread of the rust disease chemical fungicides and cultural practices are
used howerever the use fungicides to control the disease commercial plantings
significantly increases production costs it is therefore not a feasible option
in small scale soybean plantings especially in developing countries (Miles et
al., 2003). Furthermore the fungicides are expensive and are not very effective
at preventing epidemics as Bonde et al., (2006) noted yield losses of up to 50%
under severe rust epidemics with chemical control. Other legumes that also form
an integral part of the cropping system such as cowpea, pigeon pea and common
beans are functional alternative hosts of P. pachyrhizi which makes control a
great challenge (Anon, 2007; Slaminko et al., 2008). Cultural practices like
destruction of alternate hosts, timely irrigation, early planting and growing
early maturing cultivars can also reduce the incidence of the disease
(Akinsanmi et al., 2001). However, the rapid spread by wind-borne
urediniospores and the large number of host species increases chances of
soybean rust survival making cultural practices relatively ineffective (Hartman
et al., 2005).
Planting of disease
resistant cultivars is the most viable way to manage soybean rust disease. To
identify rust resistant cultivars soybean plants must be screened for
resistance to diverse pathogen populations (Twizeyimana et al., 2007). This
study therefore aims at screening selected soybean varieties commonly grown in
Kenya for resistance to soybean rust isolates under green house conditions.
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