On farm performance and farmers evaluation of cassava brown streak tolerant variety Kiroba in the Eastern zone of Tanzania

Cassava Brown Streak Disease (CBSD) is a very serious disease in many cassava growing areas of the Eastern zone of Tanzania. It is mainly confined to the lower elevations, mainly along the coast yield losses of up to 74% occur as a result of CBSD infection in some part of the Eastern zone. In the year 2001, a variety believed to be tolerant to CBSD was introduced in two villages Zogowale and Viziwaziwa in the Eastern zone in which CBSD is a big problem. The objective was to find out whether Kiroba will be tolerant to CBSD in these villages and later on replace the available susceptible varieties. The variety was planted in 5 farmers fields in each village. After one year the variety was harvested in each field 15 plants selected randomly were uprooted. Roots were assessed on CBSD incidence and severity and farmers' view on CBSD and other pest problems were ranked using a scale with classes from 1-9 (1 - Most important problem, 9 - Least important problem). The performance of the variety was also ranked by asking farmers whether it was good, poor or moderate in comparison to their commonly grown varieties. At harvesting disease severity on the roots of Kioba was found to be very low (less than class 3) in both villages an indication that it can be a good variety in CBSD prone areas. In all villages CBSD was considered to be among the major cassava production problems. While in Zogowale it was ranked as the second production problem, in Viziwaziwa it was ranked as the most serious problem. In both villages majority of farmers were of the opinion that Kiroba is a good yielder and tolerant to both CBSD and cassava mosaic disease (CMD). Farmers also considered it to be tolerant to cassaval mealy bug, a pest of cassava. Results obtained from this study indicate that Kiroba is a promising tolerant variety to CBSD and it is preferred by farmers, thus it should be introduced in other areas in the Eastern zone where CBSD is a serious problem

Effect of leaf harvesting frequency on growth and yield of sweetpotato in the Lake Zone of Tanzania

The objectives of this study were to assess the effects of leaf harvesting frequency on growth and yield of sweetpotato (Ipomoea batatus L.); to determine the suitable varietal types for use as source of leaf vegetable and to determine the suitable leaf harvesting frequency(ies) for reduced detrimental effects on growth and yield of sweetpotato. Two narrow leafed varieties Budagala and Mwananjemu and two broad leafed varieties SPN/O and Biganana were used in a randomised complete block design with 3 replications. Plot size was 8.4 m2 . Tip cuttings of 20 cm long were used as planting materials. The fully expanded top and tender leaves were plucked, counted and weighed. Tender leaves were harvested once, twice and three times during the growing period. Results showed that there were small differences between varieties and harvesting frequencies, however, harvesting at one month intervals for three times gave the highest leaf vegetable production although the yield was affected tremendously. Harvesting twice in a growing period proved the best in leaf production as well as root yields. Overall, there were significant differences between varieties and harvesting frequencies. Key Words: Ipomoea batatus, leaf harvesting, Tanzania, tuber and vine yields (African Crop Science Journal 2001 9(1): 97-103

Damage reduces shelf-life of sweetpotato during marketing

Although sweetpotato is primarily grown for home consumption, marketing is becoming increasingly important, and in this case, short shelf-life of the roots is a major constraint. An assessment of the levels of damage of sweetpotatoes when they arrive at urban markets indicated that between 49% and 93% roots exhibited some form of damage. The major types of damage noted were breakages, cuts, infestation by weevils (Cylas spp.), rotting and superficial scuffing. All forms of damage, except superficial scuffing, lead to a shortened shelf-life due to both increased fresh weight loss and rotting. Superficial scuffing increased the rate of rotting but not of weight loss. It was estimated, based on the six cases considered, that the damage resulted in a reduction of shelf-life of between 23% and 47%. Key Words: Ipomoea batatus, post-harvest losses, Tanzania (African Crop Science Journal 2001 9(1): 301-308

Sweetpotato infestation by Cylas spp. in East Africa: II. Investigating the role of root characteristics

The response of the sweetpotato weevil Cylas puncticollis (Coleoptera: Brentidae) to roots of different sweetpotato cvs was investigated as part of a project to examine the factors that affect susceptibility of sweetpotato cvs to weevil infestation in the field. Laboratory experiments were conducted at two sites (Ukiriguru and Kibaha) in Tanzania and at one site (Serere) in Uganda to determine if the harvested storage roots of sweetpotato cvs differed in their acceptability to C. puncticollis or if any root antibiosis towards C. puncticollis existed. For all experiments cultivar effects for the total number of emerging adults were significant to at least 10% and in most cases were much more significant. At Ukiriguru and Kibaha, the results showed reasonable consistency between years, and of the four cultivars used at both sites, fewer C. puncticollis adults emerged from roots of Sinia and Budagala than from SPN/0 and Mwanamonde on all occasions. A relationship between laboratory experiments and crown damage by Cylas spp. in the field suggests that cultivar differences in attraction/deterrence for Cylas spp. exist. However, correlations between adult emergence in laboratory antibiosis experiments and field infestation levels were generally not strong. Although this indicates that cultivar selection by laboratory experiments is not a useful strategy for reducing field infestation, there may be potential for using such techniques to select cultivars that are resistant to attack during longterm storage

Sweetpotato infestation by Cylas spp. in East Africa: I. Cultivar differences in field infestation and the role of plant factors

Sweetpotato weevils (Cylas spp.) constitute a major constraint upon sweetpotato production and utilization world-wide. Attempts to breed for resistance to Cylas spp. have had limited success. However, there are reports of variation in the susceptibility to weevil attack in the field among cultivars in East Africa. Field trials were conducted at two sites (Ukiriguru and Kibaha) in Tanzania and at one site (Serere) in Uganda to determine the extent to which sweetpotato cultivars presently available in East Africa consistently differ in their susceptibility to field infestation by Cylas spp. and to identify the plant factors that determine the levels of susceptibility. Several methods to assess levels of field infestation were tested, and their relative merits are discussed. Significant cultivar differences in susceptibility to Cylas spp. infestation were observed for four out of six trials carried out over 2 years. The exceptions were cases where infestation levels were either very low or very high. Linear regression models of infestation suggest that the following plant characteristics are associated with low susceptibility to Cylas spp. infestation: increased distance of roots from the soil surface, fewer soil cracks, fewer exposed roots and a high foliage yield. Both the distance of the roots from the soil surface (shortest weevil distance) and foliage yield differ significantly between cultivars. The former cannot be approximated by measurement of root neck length, but must be measured in situ