Sweetpotato (Ipomea batatas L.) is grown widely from tropical to temperate regions and is an important food security crop in tropical countries. In Africa, sweetpotato is infected by RNA viruses of many taxa (4), but DNA viruses, such as the genus Begomovirus (family Geminiviridae), infecting sweetpotatoes in the Americas have been reported only in Kenya (3). A caulimo-like DNA virus (family Caulimoviridae) has been detected in sweetpotatoes in Uganda (1). Recently, two novel badnaviruses (genus Badnavirus, family Caulimoviridae) and a new mastrevirus (genus Mastrevirus, family Geminiviridae) were discovered in a local sweetpotato cultivar maintained in a germplasm collection in Peru (2) but were not reported elsewhere. This study examined the possible existence of these novel viruses in landrace sweetpotato varieties grown in Tanzania. Nine landrace sweetpotato varieties and one introduced cultivar (NIS 91 from the International Potato Centre, Peru) were sampled from six regions of Tanzania. DNA was extracted (2) and amplified by PCR using primers (MastvKF: 5′-GACAGACCCCTAGGGTGA-3′; MastvsR 5′-ACTGCATATAGTACATGCCACA-3′) designed in this study to amplify partial, putative movement and coat protein gene sequences of Sweetpotato symptomless virus 1 (SPSMV-1) (GenBank Accession No. FJ560945) (2). Products of the expected size were detected in seven samples (varieties Ex-London, Ex-Lyawaya, Gairo, Hombolo, Kagole white, Mbeya, and Shangazi) representing four regions surveyed (Dodoma, Mbeya, Morogoro, and Kagera). PCR products from five samples were sequenced (396 nt; GenBank Accession Nos. HQ316938 to HQ316942) and found to be identical to each other and the isolate described originally in Peru (2). Amplification with primers (BadnaBKF: 5′-CAAATTAGGAGGCAGATAAATG-3′; BadnaBsR: 5′-GGTCTTCTTATGTTCCACCTT-3′) designed in this study according to the sequence of Sweetpotato virus B (SPBV-B) (GenBank Accession No.FJ560944) resulted in products of the expected size in three samples (varieties Ex-Lyawaya, Gairo, and Hombolo collected in Mbeya, Morogoro, and Dodoma, respectively) that were positive also for SPSMV-1. Sequences of the products (787 nt; HQ316935 to HQ316937) were nearly identical (99.4%). They were 96.8 to 96.9% similar to a region (nts 830-1616) of Sweetpotato virus A (SPBV-A; FJ560943) (2), whereas they were only 83.2 to 83.6 % similar to the corresponding region (1,486 to 2,272 nt) of SPBV-B (FJ560944) (2). No virus was detected in cv. NIS 91. All plants sampled exhibited mild mottling or mosaic symptoms, but a contribution to the symptoms by other untested viruses cannot be excluded because few of the large number of sweetpotato viruses have been studied in Africa (4). To our knowledge, this is the first report of SPSMV-1 and SPBV-A outside South America and in sweetpotatoes grown in the field. The results show that the two viruses are distributed widely in local sweetpotato varieties in Tanzania, which suggests that they may be found in other sweetpotato-growing areas where they have not been studied. While the yield losses caused by SPSMV-1 and SPBV-A remains to be studied, the data from this study are of practical importance in terms of regional and international exchange of sweetpotato germplasm. References: (1) V. Aritua et al. Plant Pathol. 56:324, 2007. (2) J. F. Kreuze et al. Virology 388:1, 2009. (3) T. Paprotka et al. Virus Res. 149:224, 2010. (4) F. Tairo et al. Mol. Plant Pathol. 6:199, 2005.

Whitefly (Bemisia tabaci), a major pest and vector of viruses in cassava, is the greatest current threat to cassava production in sub-Saharan Africa (SSA). Research efforts have focused on management of the two viral diseases: cassava mosaic disease (CMD) and cassava brown streak disease (CBSD), and have ignored the whitefly vector that is driving the spread of the viruses, causing CMD and CBSD in SSA. The objective of this study was to evaluate cassava genotypes for resistance to B. tabaci based on field infestation and damage in Uganda. The study was carried out in four sites with diverse agroecologies including: Namulonge, Kasese, Ngetta and Serere during 2015 and 2016.Whitefly nymph abundance and feeding damage were assessed on each test genotype from 3 to 6 months after planting (MAP). In 2015, the highest broad sense heritability estimates were 39% (4 MAP) and 53% (5 MAP) for whitefly nymph abundance and feeding damage, respectively. In 2016, broad sense heritability estimates were 23% (3 MAP) and 41% (4 MAP) for whitefly nymph abundance and feeding damage, respectively.Analysis of variance of whitefly nymph abundance showed a significant (P< 0.05) location × genotype × season interactions at 3, 4, 5 and 6 MAP. There were also significant (P< 0.05) location × genotype × season interactions at 3 and 4 MAP for whitefly feeding damage. Ten genotypes showed good levels of resistance to whitefly infestation and feeding damage including: UG120202, UG120174, NASE13, UG120160, UG120286, UG120293, UG130075, CSI-142, CS1-144 and UG130085. These genotypes may serve as parental materials for breeding programmes for whitefly and viral disease control.

A total of 57 sweet potato genotypes with high dry matter content and resistant to sweet potato virus disease (SPVD) were characterized using four simple sequence repeat (SSR) markers. The germplasm included 20 genotypes identified as having high dry matter content and 25 accessions tolerant to SPVD in a study conducted in Tanzania in 2008. The total number of alleles within the 57 genotypes across 4 loci was 395, with an average of 4 alleles per locus. The unweighted pair group method with arithmetic mean (UPGMA) and analysis of molecular variance (AMOVA) using generated SSR data, grouped the 57 genotypes into two major clusters, with mean pair-wise genetic distance of 0.55. No specific grouping was observed in relation to SPVD resistance, dry matter content and geographic location. The four microsatellites markers distinguished the 57 Tanzanian sweet potato genotypes into two major clusters. The relatively high level of genetic diversity indicates broad genetic base for sweet potato breeding in Tanzania. The results obtained demonstrate the efficiency of SSR marker technique for the assessment of genetic relationships and distinguishing between Tanzanian sweet potato genotypes. The findings of this of this study, provide valuable information to breeders to facilitate cost effective germplasm conservation and development of improved sweet potato varieties resistant to SPVD and containing high dry matter.

The five winter wheat genotypes were evaluated based on Normalized Difference Vegetative Index (NDVI) under irrigation and rain fed conditions. The 30 treatments were appropriately conducted according to the experimental design during the two consecutive cropping seasons, from 2017 to 2019. The NDVI was used to evaluate the differences of wheat genotypes from irrigation and rain fed effects. The results indicated that NDVI varied at all vegetative stages and there were some significant differences ( p < 0.05) on NDVI indices among genotypes throughout the growth period and were critical at the booting and grain filling stages from the end of March to mid-May but indices values started to decrease immediately after physiological maturity. In the entire study, the maximum NDVI (0.82) from Zhongmai-36 genotype corresponded to grain yield (8.05 Mgha− 1) and was obtained in one supplementary irrigation treatment. The maximum NDVI in rain fed treatment was (0.78) from Zhongmai-36 and corresponded to the grain yield of (7.28 Mgha− 1). This study suggests that, wheat genotype (Zhongmai-36) among the other four, can be prioritized to grow under limited irrigation applications without compromising grain yield (GY). Moreover, since the NDVI, leaf area index (LAI) and GY related positively during the entire growth period, hence can be used for the real time wheat growth monitoring, in season water requirements and grain yield simulation. This information can be used by agricultural stakeholders and decision makers on food security for early warning.