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The development of drought tolerant maize has been limited by the suggested complexity of the environment on drought phenotypic traits. However, some simple sequence repeats (SSRs) molecular markers linked to drought tolerance via quantitative trait loci (QTL) have been identified in maize but their use requires validation on newly developed elite maize inbred lines. This study therefore aims to validate 19 selected SSR markers linked to maize drought tolerance and determine the genetic diversity of sixty-eight elite maize inbred lines. Genomic DNA was extracted with a CTAB method and the PCR products were separated on agarose gel with auto radiograms visually scored for polymorphic bands to establish a data matrix. Assessment of the genetic links among the inbred lines was carried out using cluster analysis. The 68 maize inbred lines were clustered based on a matrix of genetic similarity Jaccard using the UPGMA algorithm. Some of the markers that were informative included P-bnlg238, Phi037, P-bnlg1179 and Umc2214 and these showed significant group differentiation among the inbred lines. Marker Umc1447, Umc1432 and Umc2359 were among the markers with monomorphic bands, while Phi034, Bnlg1074 and P-umc1542 showed no characterized bands. The polymorphism information content (PIC) value of the informative markers ranged from 0.13 (Bnlg434) to 0.76 (P-bnlg238). The cluster analysis classified the maize inbred lines into four groups based on the SSR data. The exploitation of information of genetic diversity among the inbred maize lines to develop drought tolerant hybrids is hereby discussed.

The rice blast (Magnaporthe grisea) is a serious constraint to rice production in many rice producing countries including Uganda. Yield losses of up to 100% are attributed to the blast disease in different rice growing regions. In addition to these, the inheritance of resistance to the disease has not yet been studied under Ugandan condition. Experiment was conducted under controlled conditions by using three resistant and four susceptible elite genotypes as parental lines for population development in half dialled mating design with the aim of providing relevant genetic information as a contribution towards the development of rice varieties with resistance to blast disease. A total of 18 crosses were advanced to F2 level. The F2 segregates and their corresponding parents were evaluated in the screen house against single virulent isolate of rice blast pathogen in 4 by 7 alpha lattice design in three replications. These results showed that there was significant variation for rice blast resistance among genotypes. Significant general and specific combining abilities were observed, indicating that both additive and non-additive gene effects were important for rice blast resistance, although the additive effect was predominant. A High coefficient of genetic determination in the broad sense (0.99) and narrow sense (0.85), were obtained on a genotype mean basis with a high Baker’s ratio of 0.86, indicating primarily additive inheritance among crosses. The segregation pattern for resistance to rice blast showed single dominant gene in some elite susceptible × resistant crosses, duplicate recessive epistasis in other elite susceptible × resistant crosses and two genes with duplicate dominant epistasis in resistant × resistant crosses. The crosses between susceptible by susceptible genotypes did not show segregation. Overall, resistance was highly heritable, with mainly additive gene action between crosses. Results suggest that simple breeding strategies with selection in early generations would be effective for rice blast resistance.

To improve on the efficiency of Quality Protein Maize (QPM) breeding in Uganda, the utility of three simple sequence repeats (SSR) markers (phi057, phi 112 and umc1066) in selection and introgression of the opaque-2 (o2) gene was investigated. Genomic DNA of six normal and seven (QPM) lines was analysed using a standard PCR protocol. Polymorphisms were detected in the 0paque-2 locus among all the maize lines when using the SSR primers, phi057 and phill2, while no polymorphism was detected with primer umc1066. To facilitate background selection in the heterozygous BC2 progeny, key phenotypic characters of the recurrent parent ( 136R) were used as additional markers. The SSR marker phi057 was co-dominant while ph-ll2 was dominant. The polymorphic SSR markers correctly predicted the expression of tryptophan in kernels of all QPM inbreds and five of the six non-QPM inbred lines. However, one non-QPM inbred line (PED49B) had a tryptophan content that is characteristic of the o2 mutation (0.090), suggesting that another genetic system may be responsible for the expression of trytophan in this maize line. Phi057 was employed to monitor the introgression of the o2 allele from CML176 to 136R. Of the 200 BC1F1 (l36R/CML176//136R) plants genotyped, 104 were found to be heterozygous, producing products corresponding to both alleles (o2 and O2), while 96 produced a single band corresponding to the homozygous dominant (O2O2) condition. The ratio of the two groups in the backcross (BC) population was consistent with the proportion 1:1 accorded by the Chi-square test (X2=0.16< X2 0.05=3.84)'for a single gene in a BC population. Therefore, under the conditions of PCR used, SSR markers phi057 and phi 112 will constitute the framework for marker assisted introgression of the o2 trait into suitable maize genotypes in Uganda. Key Words: QPM, tryptophan, Uganda, Zea mays

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The role of gbssI and gbssII genes, encoding granule bound starch synthase enzyme I and II, respectively, in quality protein maize (QPM) were studied at different days after pollination (DAP). Total RNA was used for first strand cDNA synthesis using the ImpromIISriptTM reverse transcriptase. No detectable levels of gbssI were observed. The results showed a gradual increase in expression of gbssII from 6 to 30 DAPS and gbss expression was higher in non-QPM than QPM material. Modification level 1 and 2 had lower expression levels than level 4. In general, grain endosperm opaqueness modification is rated on a scale of 1(completely hard / vitreous) to 5 (soft opaque). Overall, this study showed that gbss activity, based on its isoform gbssII was high at 30 DAP when maximum accumulation of amylose occurs. It was generally compromised in QPM than in non-QPM materials and appeared to be influenced by opaque donor parent. Protein analysis revealed a mar ked increase of GBSS in both QPM and non QPM. There was a higher proportion of GBSSII than I extracted from developing endosperm in both QPM and non QPM. At 18 DAP, the amounts of extractable GBSSII and I were lower in modified maize line 4 comparable to amounts in level 1 modified germplasm. In contrast, at 30 DAP; the GBSSII and I proteinquantities at level 2 were lower than level 4, but comparable to level 3. The major finding was that transcript use was unreliable because the genes under study (gbssI and II) were influenced by other non-allelic interactions. The stability of both GBSS and zein proteins coupled with the use of SDS-PAGE implied that only one was more reliable and required further validation. It was clear from this study, that kernel modification was regulated by complex genetic interactions. Fairly distinct systems such as the starch synthases, zein proteins and perhaps other non-allelic genetic systems all appeared to act in a complementary manner to regulate kernel texture.Key words: Amylose, protein maize, zein proteins

Nine major sorghum growing agro-ecologies of Uganda were surveyed to establish the sorghum anthracnose incidence and severity. Hierarchical sampling was used. Severity of anthracnose in the field was rated on a scale of 1-5 where 1= low severity and 5 = high severity. Analysis of Variance (ANOVA) results showed that there was variation in incidence and severity sorghum anthracnose disease. Both incidence and severity varied significantly (P

Colletotrichum sublineolum, the causal agent of sorghum anthracnose, presents high variability, genetic instability and host specialisation, hence rapidly breaking down resistance. In Uganda, no population studies of Colletotrichum sublineolum have been reported hence there is limited information on the nature of epidemics and pathogen. The present study aims at investigating the genetic diversity within 124 Colletotrichum sublineolum isolates from Uganda. The intersimple sequence repeats (ISSR) produced 37 polymorphic loci and neighbor-joining analysis revealed two major groups. There were no major groups among all isolates in studies. Analysis of molecular variation (AMOVA) based on 7 agro-ecologies of Uganda revealed the presence of a population structure, (FFST = 0.08 P = 0.05) leading to acceptance of null hypothesis stating a presence of population differentiation between the agro-ecologies in Uganda. Gene flow between agro-ecologies was 5.75 calculated from ÔFST. The results of the AMOVA analysis revealed the allelic variation (92.5%) was shared between populations. Average gene diversity over all loci ranged from 0.192 to 0.335 showing high diversity within population rather than between populations. The numbers of polymorphic loci were similar for the population studied.Key words: Colletotrichum sublineolum, ISSR, molecular markers, sorghum, strains

Common bean (Phaseolus vulgaris L.) varieties that are high yielding and drought-tolerant are crucial in coping with the effects of drought, that is prevalent among small scale producers living in Uganda. The objective of this study was to assess the level of drought tolerance in bean genotypes to be used for the initial development of drought-tolerant genotypes in Uganda. Three local genotypes and five exotic drought-tolerant lines werephenotyped under well-watered and drought-stress conditions. Drought tolerant genotypes were selected basing on high value for the geometric mean for seed yield and low drought susceptibility indices. The exotic lines, SEN 98, SCR48 and SEN 99, emerged superior in these attributes, and in pod partitioning index (PPI) and pod harvest index (PHI). Thus, these genotypes could be useful sources of genes for drought tolerance in the bean breeding programme in Uganda. The local genotype, NABE 15 was similar to the three promising materials for PPI and PHI. Pods per plant and seed weight were the yield components most affected by drought, with reductions of 82 and 78 %, respectively, for SEN 98.Key Words: Drought tolerance, Phaseolus vulgaris, phenotype

Groundnut Rosette Virus disease (GRD) has long been regarded a major limiting biotic constraint to groundnut production in Sub-Saharan Africa (SSA). The disease is caused by a complex of three viral components that interact in a synergistic fashion resulting into severe crop losses. A study was conducted to better understand the genetics of inheritance of GRD resistance. Nineteen groundnut genotypes among which twelve F2 families populations arising from a 3x4 North Carolina II mating design, were evaluated for their percentage disease severity (PDS) and incidence (PDI). There was significant genetic variability for resistance to GRD among the materials studied with more significant additive gene action as compared to non additive. However, since specific combining ability effects were not so consistent among the F2 family populations, evaluation and testing of progenies alongside with their parents would be more meaningful and selection in the early generations would be the most effective strategy. Further, narrow sense heritability of 53% suggests that prerformance of groundnut progenies could be partly predicted by both parental and individual cross means.Key Words: Arachis hypogaea, disease severity, inheritance, heritability

There has been much emphasis on breeding for increased sweetpotato storage root yield, but less on dry matter yield, and its inheritance. High dry matter content (DMC) is associated with consumer preferences, and is important for the processing industry. This study was conducted to determine the type of gene action controlling DMC and to assess genotype by environment (G x E) interaction effect on DMC in sweetpotato. Five parental clones varying in DMC were hand-crossed in a half-diallel design to generate ten families. Ten genotypes of each family were planted in a trial at Namulonge (swamp and upland environments) and Serere in Uganda in 2009 and 2010. Highly significant (P

Rice bacterial blight (Xanthomonas oryzae pv.oryzae) is a major constraint to rice (Oryza sativa L.) production in Uganda and as part of strategies to develop resistant cultivars, it is important to evaluate resistance of commonly used cultivars. A full-diallel mating design involving three resistant and three susceptible rice cultivars was used to produce F1 and F2 progenies in a screen-house at the National Crop Resources Research Institute (NaCRRI), Namulonge in Uganda. The parents and F2 populations were challenged with the Xanthomonas oryzae pv.oryzae isolate (UX00) and lesion lengths were scored 21 days after inoculation (DAI). Griffing’s combining ability analysis showed significant specific combining ability (SCA) and non-significant general combining ability (GCA) effects, indicating the preponderance of non-additive gene effects in controlling the resistance to bacterial leaf blight (BLB) in rice. Rice genotypes, NERICA14, NERICA10 and NERICA4 had desirable GCA estimates, and were, therefore, the best general combiners. Crosses CO39 x NERICA10 and NERICA14 x IRAT104 had favorable SCA values. These hybrids are thus, promising in developing the BLB resistant progenies. Significant reciprocal effects indicate the importance of maternal contribution in controlling the BLB virulence. For this, resistant lines can be used as female parents for fear of affecting transfer of resistance to the progenies, and the hybrids and their reciprocals would be handled separately. Low estimates of narrow sense coefficient of genetic determination (NSCGD) (0.9%) and medium broad sense coefficient of genetic determination (BSCGD) estimates (16.4%) highlight the influence of non-additive gene action in controlling the resistance to BLB, confirming an effective selection of superior genotypes at advanced generations when the maximum homozygosity is fixed.Keywords: Gene action, Oryza sativa, Xanthomonas oryzaeAfrican Crop Science Journal, Vol. 20, Issue Supplement s1, pp. 105 - 112

Rice (Oryza spp.) has long been an important food staple for many traditional rice growing communities. Key developments in efforts to improve rice production such as the development of NERICA varieties have been widely recognised. Nonetheless, emerging diseases such as the Rice Yellow Mottle Virus sobemovirus (RYMV) undermine dissemination of new technologies and sustained productivity of the crop. The RYMV is highly variable and several resistance-breaking strains have been identified. Appropriate sources of resistance to RYMV should be identified and characterised in order to pyramid genes for both complete and partial resistance. In this study, reaction of nine (9) rice cultivars to RYMV virulent strain in Uganda was determined. Four upland and three lowland NERICA varieties, an O. Sativa lowland variety, Gigante and IR64 were observed. Isolates of RYMV were collected from three “hot-spots” in Uganda (Lira, Luweero and Iganga). The isolate from Iganga was most virulent on RYMV susceptible cultivar (IR64), and thus used to constitute study treatment evaluated in the study. Cultivars were potted and raised in a screenhouse experiment arranged in a randomised complete block design (RCBD) with three replicates. Significant differences for relative area under disease progress curve (RAUDPC) (P ≤ 0.01) were detected among the cultivars. Similarly, significant positive correlations (P ≤ 0.05) were observed between mean disease score and percentage reduction in grain weight and between percentage grain weight and reduction in plant height. Susceptible cultivars were characterised based on premature death, and significantly reduced grain weight and plant height (P ≤ 0.01 and P ≤ 0.05), respectively. These results demonstrated the aggressive nature of the specific RYMV strain, and provided evidence with regard to the importance of grain weight and plant height in evaluating RYMV disease resistance.Keywords: Grain weight, NERICA, plant height, Oryza sativa, susceptible cultivarsAfrican Crop Science Journal, Vol. 20, Issue Supplement s1, pp. 51 - 57

Fusarium root rot (FRR), caused by Fusarium solani f.sp. , is one of the most serious root rot diseases of common bean (Phaseolus vulgaris L.) throughout the world. Yield losses of up to 84% have been attributed to the disease. Development and deployment of resistant materials is the most feasible approach to managing the disease. The objective of this study was to estimate the number of pyramided Fusarium root rot resistance genes among the four resistant lines and determine their effectiveness in improving levels of resistance to Fusarium root rot in the susceptible bean cultivars. Crosses among four Fusarium root rot (Fusarium solani f.sp. phaseoli) resistant common bean (Phaseolus vulgaris) were developed. They involved six inbred lines, MLB-48-89A (M48), MLB-49-89A (M49), G2333 (G2) and G685 (G6), and two susceptible cultivars, K20 and Kanyebwa, The resistant lines were used to develop a double cross (DC) population. The DC F1 and each resistant parent were crossed to each of the two susceptible cultivars to form five-parent and single crosses, respectively. Developed populations were subjected to Fusarium solani f. sp. phasoeli isolate-3 under screenhouse conditions. There were segregation ratios of 15:1 (χ2 = 1.89, P = 0.17), 61:3 (χ2 = 0.18, P = 0.67) and 249:7 (χ2 = 1.74, P = 0.19) indicating that two, three and four genes independently condition resistance to F. solani in lines G2 x G6, M49 x M48 and (M49 x M48) x (G2 x G6). A good fit of only four genes in the double cross compared to two in the G2 x G6 , and three genes in the M49 x M48 cross suggests that at least one parent in the G2 x G6 cross have the same or closely linked genes as a parent in the M49 x M48 cross. The F1 means of the five-parent cross (FPC) involving either susceptible parent had lower disease scores, though not significantly (P > 0.05), than the single-crosses from that parent. The F2 of both FPC showed less disease than the single-cross (SC) means (P < 0.05) compared to the single-cross (SC) while the F2 of both FPC had a significant negative deviation (P < 0.05). The F2 frequency distributions also showed that the FPC in both Kanyebwa and K20 populations had higher proportions of resistant plants than any of the single crosses in the respective populations. The superior performance of the FPC over the SC demonstrates that combining resistance genes form different FRR resistance sources can provide a stable source of resistance than using single sources of resistance.African Crop Science Journal, Vol. 20, Issue Supplement s1, pp. 1 - 13

Cassava mosaic disease (CMD) resistant varieties have been used to manage CMD in Uganda. In spite the availability of a number of CMD resistant cultivars, several local landraces are continually grown in Uganda because they possess certain desirable traits, which may not have been fully met by the resistant varieties. Field based trials were setup to evaluate the response to CMD of some landraces that became prominent after the 1990s CMD pandemic. Experiments were located in areas where CMD is reported to have subsided namely, Mukono (Central Uganda) and Bulindi (Western Uganda). Three landraces were evaluated per site along with resistant (Nase 4) and susceptible (Bao) standards. Plots were planted with materials obtained from either diseased or healthy fields. The results showed differences in sensitivity to CMD among varieties tested, with landraces consistently having higher CMD incidences than Nase 4. The landraces tested in Mukono were more susceptible to CMD than even the Bao, while at Bulindi on the other hand, only Sibampale proved to be more resistant than Bao. There were differences in the whitefly populations among the cassava varieties and locations. High whitefly populations characterized all landraces and Nase 4. In most tested varieties, there was a higher infestation of whiteflies on healthy than diseased plants. Low spread of CMD among local landraces was observed in Bulindi as would be expected in areas where CMD has almost subsided (low pressure areas). However, in Mukono, disease spread among landraces was very rapid and high CMD incidences reaching 100% were recorded regardless of whether plots were planted with healthy or diseased cuttings suggesting it to be a CMD hot-spot. Thus, the use of clean planting materials as an effective phytosanitary method can only be employed under low disease pressure while high disease pressure areas need use of resistant varieties.