INTROGRESION OF MAIZE STREAK VIRUS TOLERANCE INTO SELECTED PHOSPHORUS EFFICIENT AND ALUMINIUM TOLERANT KENYAN MAIZE LINES

Abstract

Maize is one of the most important cereals produced globally. It has a number of uses such as the production of feed, food, as well as industrial products. However, its productivity is limited by both biotic and abiotic stresses, with phosphorus (P) deficiency, aluminium (Al) toxicity and Maize Streak Virus (MSV) contributing significantly to its yield loses. The objective of this study to was to improve maize yields by developing locally adaptable maize lines that combine maize streak virus tolerance to aluminium toxicity and P-deficiency tolerance. Fifty-seven single crosses were developed and thirty-one screened for Aluminium tolerance in solution culture containing 0 and 222 µM Al for 3 days. All the crosses were further screened in the field together with checks for low P tolerance at 2 P levels (0kg P/ha and 26kgP/ha P) at Bumala. The crosses and checks were further screened for MSV tolerance in the field at Maseno and in the greenhouse at Muguga. The 222µM Al treatment significantly inhibited root growth in 90.4% of the genotypes in the study (<0.001). However, for 9.6% of the genotypes, exposure to the solution media induced root growth. Majority of the F1 58.1% were susceptible to Al toxicity, while only 22.6% and 19.4% were categorised as tolerant and moderately tolerant respectively. This low tolerance to Al toxicity was also exhibited in low heritability (0.16) obtained for RNRG. Of the F1, 46.6% were heterotic based on mid-parent heterosis and better parent heterosis for Relative Net Rot Growth. The genotypes varied significantly with regard to grain yield, plant height, ear height and other traits under the two Phosphorus treatments. The best single cross under no P based on grain yield was 203B-9X13MAK-54 (1.1820 t/ha), while the worst was KML036X13MAK-1B giving no grain yield completely. Under 26kg/ha P, the best single cross was 13MAK9BX203B (2.291 t/ha) and the worst was POOL9BASF-3X13MAK-9B (0.22 t/ha). Overall plant height (PH) and ear height (EH) had a strong positive correlation (r = 0.96), while both EH (r = 0.50), and plant height (r =0.63) had moderate and positive correlation with grain yield at Bumala for all genotypes. At Maseno, there was a strong and positive correlation between plant height and ear height (r= 0.93), between plant height and grain yield (r=0.87), and between ear height and grain yield (r=0.80) for all genotypes. Under the greenhouse experiment most of the genotypes (97.6%) were susceptible to MSV, including the South African material that were supposedly MSV tolerant. Only Olerai, a Kenyan cultivar, and POOL9BASF-3 were tolerant to Kenyan MSV, and only one single cross 13BXPOOL9BASF-3 was moderately tolerant to MSV. These results could be due to the possibility of new MSV strains causing infection in Kenya, or the variation in strains between Kenya and South Africa which was the source of MSV tolerance. The single cross 13BXPOOL9BASF3, was also identified as moderately responsive to P addition, but P inefficient. This study identified one outstanding line with multiple tolerance to P and MSV, and a few with P, AL, MSV tolerance that can be used for maize improvement due to soil acidity and MSV tolerance.