Agronomic performance and breeding potential of selected maize inbred lines for improvement of protein quality of adapted Ugandan germplasm
Kalule, Okello David
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The main objective of this study was to characterise selected QPM inbred lines obtained from CIMMYT under Ugandan conditions. Agronomic performance and combining abilities were determined to assess the breeding potential of these materials. A total of 12 maize inbred lines were evaluated. Nine of these, namely: CMLL44, CMLl59, CML 173, CML176, CML181, CML 182, CML387, CML395 and CML444 were obtained from CIMMYT. The first six CIMMYT inbred lines were QPM inbred lines and the latter 3 were normal maize inbred lines known to have some good traits. Also included in the evaluations were three recycled lines from the National Cereals' programmes. These were PED 49A, PED 498 and 136R that have been improved for tolerance to drought, MSVD, TLB and also found to have good combining abilities. Experimental plots for this study were planted at Namulonge Agricultural and Animal Production Research Institute (NAARI) in Central Uganda, which is considered a hot spot for several foliar diseases of maize, namely, the Maize streak virus disease (MSVD), Turcicum leaf blight (TLB), the Gray leaf spot (GLS) and Leaf rust (LR). The results showed that lines CMLl59 and CML144 were the most susceptible to MSV and TLB, whereas, line CML173 was early maturing, had very good plant aspect and was moderately resistant to the major foliar diseases. Similarly, line CML176 was very susceptible to MSV, had moderate resistance to TLB, GLS and LR, but had good plant aspects, high protein quality (tryptophan content) and quantity. Line CML181 was found to be resistant to MSV and moderately resistant to TLB, GLS and rust. Unfortunately, CML181 had the lowest tryptophan level. In contrast, line CML 182 was found to be very susceptible to MSV, TLB and has a poor plant aspect. An analysis of combining abilities was performed using a 6 x 6 half diallel mating design with the QPM inbred lines as males. Estimates of both general (GCA) and specific (SCA) combining ability were made for disease tolerance using the Fl generation. The results indicated the existence of genetic divergence for all the diseases analyzed with additive effects more predominant. Promising QPM inbred lines that could be incorporated into the maize breeding programs presented good GCA for the major foliar diseases, good plant aspects and high protein quality and quantity. On this basis, lines CMLL76 and CML173 were found to be superior and, therefore, should be considered for inclusion in Ugandan QPM breeding programmes. Pedigree selection from outstanding F1s generated many segregants for various gains. For example, Line 2 had very short maturity dates (52 days to silking). Such a line could be key in helping address the increasingly water shortage due to unreliable rainfall in Uganda. Line I manifested traits distinctive of highland germplasm. Other qualities identified included tighter husk cover, which is good for protection against ear rots, plant aspect and resistance to disease. Furthermore, these segregants have been developed under local conditions at Namulonge, they are now considered adapted to Ugandan conditions. However, further multi-locations trials will be required for these early generation lines to determine the stability for the new traits. Substantial emphasis has been put into the development of hard endosperm o2 maize irrespective of the kernel texture. Differences in preference for a particular maize grain texture, however, exist among farmers and breeders yet the relationship among key grain quality attributes is not known. Thirty cobs from families of variety Longe 5 were evaluated to determine the relationship between kernel texture, level of kernel modification, protein and tryptophan content in opaque-2, and grain weight' The results showed that grain weight but not tryptophan content appears to be influenced by both kernel texture and modification. No adverse effect of kernel texture on endosperm modification was observed. Thus, grain yield maybe improved by selection for vitreousness (higher modification scores) and thereby making QPM agronomically competitive with normal-endosperrn alternatives. This study has, therefore, generated vital information for QPM breeding in Uganda. The new QPM germplasm recently brought into the country is not only better understood but novel early generation breeding lines have been generated and fairly characterised for various gains. In so doing the QPM donor base for wider environments has been increased. Additionally, the role of kernel texture on trlptophan level, endosperm modification, and grain weight/yield elucidated.