475
Eastern Kenya. The areas are hot and dry with temperatures ranging between 14 and
34 °C. Annual precipitation ranges between 500 and 1050 mm, with an average of
900 mm per annum. The areas represent some of the typical semiarid areas in Kenya
predominated by smallholder farmers where agriculture is the main stay.
Cowpea and maize are among the key crops that are grown for food and cash
generation. The two crops can be intercropped and provide balanced nutrition with
maize, a stable food in Kenya, providing carbohydrates and cowpea providing both
vitamins (leaves used as vegetables) and proteins (grains used as a protein source).
The selection of farms for the study depended on farm history, where only farms
with active cultivation of the two experimental crops and with no inoculation history were selected. Greenhouse bioassays and laboratory experiments were carried
out in Kenyatta University, Nairobi, Kenya.
2.2 Soil Sampling and Greenhouse Bioassays
This study involved greenhouse experiments and laboratory analyses. Soil samples
(20 kg) were obtained from the 10 farms (5 farms each from Embu County and
Kitui County) at a depth of 0–30 cm. The soil samples from each farm were then
dried and separated into two portions. One portion was used for analysis of physicochemical properties and the other portion used for rhizobia and AMF trapping, with
cowpea and maize as the host plant, respectively. Four rain-fed maize (Zea mays L.)
cultivars, comprising of two open pollinated varieties (M1 [OPV 1] and M2 [OPV 2]),
M3 (a landrace) and M4 (hybrid maize), and four cowpea (Vigna unguiculata (L.)
Walp.) cultivars (three open pollinated varieties (C1 [OPV 1], C3 [OPV 2], C4
[OPV 3]) and C2 (a landrace), were grown in 3-L pots in a split-plot arrangement in
a completely randomized experimental design. Each treatment was replicated four
times. The crops were irrigated as required and harvested after 40 days. The maize
crop was examined for AMF root colonization, while cowpea plants were tested for
the nodule dry weight and nodule number.
2.3 Isolation and Characterization of Rhizobia
Procedures described by Castellane et al. (2015) were used for the isolation of pure
rhizobia isolates from nodules of cowpeas from trapping experiments in the greenhouse. All isolates were characterized based on selected morphological features:
colony size, colour, shape, mucosity, border, elevation, transparency and capacity to
produce exo-polysaccharides. The isolates were cultured in yeast extract mannitol
agar (YEMA) media and later in YEMA containing Congo red dye and YEMA
containing bromothymol blue.
Exploiting Arbuscular Mycorrhizal Fungi-Rhizobia-Legume Symbiosis to Increase…
Eastern Kenya. The areas are hot and dry with temperatures ranging between 14 and
34 °C. Annual precipitation ranges between 500 and 1050 mm, with an average of
900 mm per annum. The areas represent some of the typical semiarid areas in Kenya
predominated by smallholder farmers where agriculture is the main stay.
Cowpea and maize are among the key crops that are grown for food and cash
generation. The two crops can be intercropped and provide balanced nutrition with
maize, a stable food in Kenya, providing carbohydrates and cowpea providing both
vitamins (leaves used as vegetables) and proteins (grains used as a protein source).
The selection of farms for the study depended on farm history, where only farms
with active cultivation of the two experimental crops and with no inoculation history were selected. Greenhouse bioassays and laboratory experiments were carried
out in Kenyatta University, Nairobi, Kenya.
2.2 Soil Sampling and Greenhouse Bioassays
This study involved greenhouse experiments and laboratory analyses. Soil samples
(20 kg) were obtained from the 10 farms (5 farms each from Embu County and
Kitui County) at a depth of 0–30 cm. The soil samples from each farm were then
dried and separated into two portions. One portion was used for analysis of physicochemical properties and the other portion used for rhizobia and AMF trapping, with
cowpea and maize as the host plant, respectively. Four rain-fed maize (Zea mays L.)
cultivars, comprising of two open pollinated varieties (M1 [OPV 1] and M2 [OPV 2]),
M3 (a landrace) and M4 (hybrid maize), and four cowpea (Vigna unguiculata (L.)
Walp.) cultivars (three open pollinated varieties (C1 [OPV 1], C3 [OPV 2], C4
[OPV 3]) and C2 (a landrace), were grown in 3-L pots in a split-plot arrangement in
a completely randomized experimental design. Each treatment was replicated four
times. The crops were irrigated as required and harvested after 40 days. The maize
crop was examined for AMF root colonization, while cowpea plants were tested for
the nodule dry weight and nodule number.
2.3 Isolation and Characterization of Rhizobia
Procedures described by Castellane et al. (2015) were used for the isolation of pure
rhizobia isolates from nodules of cowpeas from trapping experiments in the greenhouse. All isolates were characterized based on selected morphological features:
colony size, colour, shape, mucosity, border, elevation, transparency and capacity to
produce exo-polysaccharides. The isolates were cultured in yeast extract mannitol
agar (YEMA) media and later in YEMA containing Congo red dye and YEMA
containing bromothymol blue.
Exploiting Arbuscular Mycorrhizal Fungi-Rhizobia-Legume Symbiosis to Increase…