Virus movement from infected sweetpotato vines to roots and reversion on root sprouts

Sweetpotato is usually propagated in Uganda by vine cuttings from mature crops, but sometimes sprouts from storage roots are used, especially in drought-prone areas. No information is available on whether the storage of roots of Ugandan cultivars are infected with the viruses and whether the sprouts on them express symptoms so that farmers can eliminate diseased ones. Information on root sprout reversion from virus infection is also lacking. The storage roots of five sweetpotato cultivars was sourced either by random selection of roots from already harvested roots or obtained from symptomless plants selected before harvest at Makerere University Agricultural Research Institute, Kabanyolo (MUARIK), and the National Semi Arid Resources Research Institute (NaSARRI). Roots were also generated in a screenhouse after being inoculated with Sweet potato feathery mottle virus (SPFMV) and/or Sweet potato chlorotic stunt virus (SPCSV). More than 70% of sprouts from roots of all the cultivars selected after harvest at MUARIK and NaSARRI were infected with the viruses. For roots obtained from symptomless plants, 64% and 21% of the sprouted roots from MUARIK and NaSARRI were infected with the viruses, respectively. Most of the root samples from MUARIK had visible virus symptoms on sprouts and tested positive for both SPFMV and SPCSV, whereas those from NaSARRI did not show symptoms and were infected primarily with SPFMV. Plants graft-inoculated with either SPCSV or SPFMV alone produced both infected and noninfected roots, whereas all the root sprouts from dually infected plants showed virus symptoms. Reversion from virus infection was observed on root sprouts infected singly with SPFMV, whereas those infected with SPCSV showed recovery only, and none of the root sprouts infected by both viruses showed recovery. This study proves that roots are good reservoirs for viruses, and reversion occurs only when singly infected with SPFMV. Therefore, there is a need to establish seed channels in which seedstock is cleaned continuously and made available to farmers

Genetic Diversity for Grain Nutrients Content in Finger Millet (Eleusine Coracana (L.) Gaertn.) Germplasm

Knowledge of existing genetic variability is essential for initiating a successful plant breeding program. This chapter reviews nutrient diversity studies conducted on finger millet germplasm globally. In all the studies, very high variability was observed in all the quality traits determined. Most of the nutrients were positively correlated with each other, implying that they can simultaneously be improved. Grain color and glume covering were associated with nutrient content, with darker grains having higher compared to white-colored and enclosed grains having higher nutrient content than intermediate covered having higher content. These two can be used as morphological markers. Local cultivars and varieties released in the East and South Asia (ESA) region had significantly lower levels of the main essential nutrients (Ca, Fe, and Zn) found in finger millet, most likely as a result of farmers selecting for varieties with brown-colored grain. Country of origin was highly significant for all the nutrients, with accessions from eastern and southern Africa having significantly lower nutrient contents. Grain color was associated with nutrient content with darker grains having higher compared to white colored. All nutrients were positively correlated (P < 0.001) with each other. Grain yield was not significantly correlated with any nutrient content. The substantial variability for the grain nutrients observed in the finger millet core collection and local germplasm indicates the possibility for the selection of nutrient-rich accessions for use in the breeding program

Development of a specific molecular tool for detecting Xanthomonas campestris pv. musacearum

A specific and rapid diagnostic tool has been developed to detect Xanthomonas campestris pv. musacearum, the causal agent of bacterial wilt of banana. PCR primers were developed from intergenic regions of X. campestris pv. musacearum following its partial sequence. A total of 48 primers were tested for specificity to X. campestris pv. musacearum strains collected from various regions in Uganda. These were also tested for specificity against related Xanthomonas species from the vasicola group, Xanthomonas species pathogenic to other crops, and against those existing saprophytically on banana plants. Seven primer sets (Xcm12, Xcm35, Xcm36, Xcm38, Xcm44, Xcm47 and Xcm48) were found to be very specific to X. campestris pv. musacearum. These primer sets directed the amplification of the expected product for all 52 strains of X. campestris pv. musacearum collected from different locations in Uganda. No amplification products were obtained with unrelated phytopathogenic bacteria or endophytic ⁄ epiphytic bacteria from banana. A detection limit of 103 CFU mL)1 corresponding to about four cells per PCR reaction was observed when X. campestris pv. musacearum cells were used for all the seven primer sets. The DNA samples from symptomless plant tissues also tested positive with primer set Xcm38. The specific PCR method described here is a valuable diagnostic tool which can be used to detect the pathogen at early stages of infection and monitor disease

Spread of Xanthomonas campestris pv. musacearum in banana plants: implications for management of banana Xanthomonas wilt disease

. Published online: 21 Oct 2013.Banana Xanthomonas wilt (BXW) caused by Xanthomonas campestris pv. musacearum (Xcm) is a devastating disease of bananas in Uganda and across the Great Lakes region of East and Central Africa. While use of disease-free suckers is recognized as important to control BXW, bacterial movement from infected mother plants to their suckers is not well understood. In this study, the movement of Xcm through the pseudostem of naturally and artificially infected bananas was examined. In naturally infected plants, samples of plant organs collected from susceptible cultivars ‘Kayinja’, ‘Nfuuka’ and Kivuuvu’ (Musa acuminata) at various stages of disease were analysed using a polymerase chain reaction assay employing Xcm specific primers. Xanthomonas campestris pv. musacearum was detected in 70% of asymptomatic corms and suckers collected from each of the three susceptible cultivars. In ‘Kayinja’ and ‘Nakitembe’, Xcm was recovered from plant parts 20 cm away from the point of inoculation prior to symptom development. The population of Xcm was variable within and among the plant parts over time, with the highest number being recorded in the inoculated region for all cultivars. No disease was observed seven days after inoculation of the Xcm-resistant wild species M. balbisiana and Xcm was restricted to the point of inoculation. This study implies that by the time wilt symptoms are expressed, Xcm has migrated from the point of entry to most parts of the plants. Use of suckers from infected plants should be restricted as they are likely to be latently infected and could thus result in disease when transplanted