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Soil acidity and phosphorus (P) deficiency are some of the major causes of low maize yields in Kenya. This study determined the immediate and residual effects of lime and P fertilizer on soil pH, exchangeable aluminium (Al), available P, maize grain yield, agronomic P use and P fertilizer recovery efficiencies on a western Kenya acid soil. The treatments were: P fertilizer (0, 26 and 52 kg P ha −1 as triple super phosphate) and lime (0, 2, 4 and 6 tons lime ha −1 ) applied once at the beginning of the study. A burnt liming material with 92.5% calcium carbonate equivalent was used. Soil samples were analysed prior to and after treatment application. The site had low soil pH-H 2 O (4.9), available P (2.3 mg kg −1 ), total N (0.17%), high Al (2.0 cmol kg −1 exchangeable Al and 29% Al saturation). Lime reduced soil pH and exchangeable Al, leading to increased soil available P. Lime at 2, 4 and 6 tons ha −1 maintained soil pH ≥ 5.5 for 2, 3 and 4 years, respectively. The study observed that the recommended P fertilizer rate (26 kg P ha −1 ) for maize production in Kenya was inadequate to raise soil available P to the critical level (≥10 mg P kg −1 soil bicarbonate extractable P) required for healthy maize growth. To maintain soil available P at the critical level where 52 kg P ha −1 and combined 52 kg P ha −1 + 4 tons lime ha −1 were applied, it would be necessary to reapply the same P fertilizer rate after every one and two cropping seasons, respectively. The 4-year mean grain yield increments were 0.17, 0.34, 0.50, 0.58 and 1.17 tons ha −1 due to 2, 4, 6 tons lime ha −1 , 26 kg P and 52 kg P ha −1 , respectively. Both agronomic P use and P fertilizer recovery efficiencies increased with increasing rates of lime and decreased with increasing rates of P fertilizer. Therefore, combined applications of both lime and P fertilizer are important for enhancing maize production on P-deficient acid soils in western Kenya.

In Kenya, maize (Zea mays L.) is mainly grown on acid soils in high rainfall areas. These soils are known for low available phosphorus (P), partly due to its sorption by aluminium (Al) and iron oxides. The study determined soil P sorption, lime requirements and the effects of lime on soil pH, Al levels and available P on the main maize growing acids soils in the highlands east and west of Rift Valley (RV), Kenya. Burnt lime containing 21% calcium oxide was used. The soils were strongly to extremely acid (pH 4.85-4.07), had high exchangeable Al 3+ (> 2 cmol Al kg -1 ) and Al saturation (> 20% Al), which most maize germplasm grown in Kenya are sensitive to. The base cations, cation exchange capacity and available P (< 10 mg P kg -1 bicarbonate extractable P) were low, except at one site in the highlands east of RV indicative with history of high fertilizer applications. Highlands east of RV soils had higher P sorption (343-402 mg P kg -1 ) than the west (107-258 mg P kg -1), probably because of their high Al 3+ ions and also the energies of bonding between the soil colloids and phosphate ions. Highlands east of RV also had higher lime requirements (11.4-21.9 tons lime ha -1 ) than the west (5.3-9.8 tons lime ha -1 ). Due to differences in soil acidity, Al levels and P sorption capacities within and between highlands east and west of RV, blanket P fertilizer and lime recommendations may not serve all soils equally well.

This review focused on the efforts made to understand and manage Kenyan acid soils by use of inorganic, organic materials (OMs) and crop germplasms tolerant to soil aluminium (Al) toxicity and/or low soil available phosphorus (P). Kenyan acid soils which occupy 13% of the total land area were developed through parent materials of acid origin, leaching of base cations and use of acid forming fertilizers. They are high in Al (>2 cmol Al/kg and > 20% Al saturation) and low in soil available P (< 5 mg P/kg soil) due to moderate-high (107-402 mg P/kg) P sorption, hence crops recover only 9.6 to 13.5% of the P fertilizer. Application of lime, P fertilizer and OMs increases soil pH, available P and reduces Al toxicity on Kenyan acid soils. Lime, P fertilizers and OMs have increased maize grain yield by 5-75, 18-93 and 70-100%, respectively on Kenyan acid soils. Similarly, deployment of crop cultivars tolerant to Al toxicity and/or low soil available P increases crop yields. However, lack of knowledge on the importance of lime, credit to purchase farm inputs, crop varieties tolerant to soil acidity constraints and inadequate amounts of OMs limits crop yield on Kenyan acid soils.

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The goal of this study was to develop an efficient regeneration protocol to be used for genetic transformation of sesame. Published regeneration methods using benzyladenine (BA) and 1-naphthalene acetic acid (NAA) were unsuccessful for the cultivars used herein. Experiments were carried out using cotyledon and hypocotyl explants from the cultivar Mtwara-2. Later the optimised culture conditions were used to investigate the regeneration response of different genotypes. There was significant interaction between hormone treatments and macronutrients for shoot and root regeneration. Results also showed that shoot regeneration was significantly influenced by explant type. Shoots were only obtained from cotyledons whereas both cotyledons and hypocotyls could produce roots. Modified Murashige and Skoog (MS) medium with N6 macronutrients resulted in twice the shoot regeneration frequency obtained with ½MS macronutrients in the presence of thidiazuron (TDZ). The shoot regeneration frequency was significantly reduced when BA was used in place of TDZ. On shoot regeneration medium containing BA and NAA, only roots were formed. Replacing NAA with indole-3-acetic acid (IAA) greatly improved the regeneration of shoots. The optimum growth regulator combination for shoot regeneration was 20 lM TDZ together with 2.5 lM IAA, which gave a frequency of 63% and 4.4 shoots per regenerating explant for the best cultivar Ex-El. Genotypic differences were significant both for the number of explants regenerating shoots and the number of shoots produced per regenerating explant.

Aluminum (Al) toxicity on acid soils adversely affects maize yields, which can be overcome by combining soil amendments with genetic tolerance. In maize, ZmMATE1 confers Al tolerance via Al-activated citrate release, whereby citrate forms non-toxic complexes with Al3+ in the rhizosphere. Here, we investigated Al tolerance mechanisms in maize germplasm originated from Kenya based on quantitative trait loci (QTL) mapping. Five QTLs and four epistatic interactions explained ~51% of the phenotypic variation for Al tolerance. The lack of Al tolerance QTL on chromosome 6 and the much lower expression of ZmMATE1 in both Kenyan lines than in Cateto Al237, which donates the superior allele of ZmMATE1, strongly indicate that this gene does not play a significant role in Al tolerance in neither parent. In turn, maize homologs to genes previously implicated in Al tolerance in other species, ZmNrat1, ZmMATE3, ZmWRKY and ZmART1, co-localized with Al tolerance QTL and were more highly expressed in the parent that donate favorable QTL alleles. However, these candidate genes will require further studies for functional validation on maize Al tolerance. The existence of Al tolerance mechanisms independent from ZmMATE1 suggests it is possible to develop highly Al tolerant cultivars by pyramiding complementary Al tolerance genes in maize.

Twenty naturally occurring male-sterile plants were recovered from a normal population of the grain amaranth, variety Jumla . The identification of the male-sterile plants is possible during anthesis and after flowering . The male-sterility in this variety is conditioned by a single recessive nuclear gene ms.