M. Mwangi

Fusarium Species from the Cassava Root Rot Complex in West Africa

ABSTRACT Fusarium species are a significant component of the set of fungi associated with cassava root rot. Yield losses due to root rot average 0.5 to 1 ton/ha but losses >3 ton/ha, an equivalent of 15 to 20% yield, often occur. This paper reviews previous work on cassava root rot and summarizes a few recent studies on Fusarium species associated with the disease. Our studies in Cameroon showed that 30% of rotted tubers were infected by Fusarium spp. 12 months after planting and represented 25% of all the fungal isolates recovered. Other commonly recovered fungi were Botryodiplodia theobromae and Armillaria spp. Numerous and diverse species of Fusarium were associated with rotted cassava roots in Nigeria and Cameroon. At least 13 distinct amplified fragment length polymorphism (AFLP) groups of Fusarium were distinguishable, each group probably a distinct species, and many of them might represent previously undescribed Fusarium species. The two largest of the AFLP groups correspond to F. oxysporum and F. solani species complex. The distribution of Fusarium spp. varied among countries and among locations within a country, suggesting that germ plasm resistant at one location may not be resistant at another. Fusarium spp. also cause seedling blight of cassava and can be recovered from the stems of infected plants up to 1 m above the ground. Therefore, the pathogen can spread with stems cut as planting material. Fusarium spp. also can colonize Chromolaena odorata, the dominant weed in short fallows, which could further complicate management efforts by serving as an alternative host for strains that colonize cassava.

Cost-effective Nutrient Sources for Tissue Culture of Cassava (Manihot esculenta Crantz)

Application of tissue culture technology is constrained by high costs making seedlings unaffordable. The objective of this study was to evaluate the possibility of using locally available fertilizers as alternative nutrient sources for cassava micropropagation. A Low Cost Medium (LCM) whereby the conventional sources of four Murashige and Skoog (MS) macronutrients had been replaced with locally available fertilizers was developed. Stanes Iodized Microfood® from Osho Chemical Industries in Nairobi was used as the alternative source of micronutrients. Modified conventional MS medium was used as the control. Both media were supplemented with 30 g/l of table sugar and 3 g/l of gelrite. Two cassava varieties, Muchericheri and KME 1 were regenerated on the two media. Node, leaf and root formation patterns plus plant height were determined and compared. A reduction of 95.50% in nutrient cost was achieved. The two cassava varieties had a significantly (p < 0.05) higher number of nodes on the conventional medium compared to LCM. There were no differences in node formation by the two varieties on the low cost medium during both initiation and multiplication. KME 1 produced significantly more leaves on the LCM compared to Muchericheri during both initiation and multiplication. Acclimatization of plantlets was successful; hence, this protocol can be adopted in cassava regeneration. Keywords: Tissue culture, cassava, nutrient sources, micropropagation, low cost medium, acclimatization

Phenotyping of Selected Kenyan Passiflora edulis Varieties and Their Hybrids Based on Quantitative Morpho-agronomic Traits

The passion fruit was introduced to Kenya through Europe in the 1920s, and only gained significant economic importance in the 1990s. Several species of the genus Passiflora present potential superior characteristics for genetic breeding of the passion fruit germplasm. Quantitative morpho-agronomic traits are important in passion fruit breeding since they allow for discrimination of varieties for important parameters that are useful in selection of fruit for market. The present study aimed at evaluating existing phenotypic variation between the Purple and Brazil varieties as well as their hybrids, developed by the Kenya Agricultural and Livestock Research Organization (KALRO). Seven quantitative morpho-agronomic traits were targeted with replication per plant and variety. Principal component technique and cluster analysis statistical tools of Minitab 17.0 software were used to discriminate the accessions under study based on the morpho-agronomic traits. Both the dendrogram and scatter plot clustered accessions based on their respective varieties, an indication of phenotypic relatedness within varieties. The results of this study will supplement the current body of knowledge on Kenyan passion fruit breeding.

Factors Affecting Technical Efficiency of Passion Fruit Producers in the Kenya Highlands

The importance of passion fruit in livelihood improvement has been a key driver among rural households production participation in Kenya. The frequency of harvest and income flows compared to other farm enterprises in the fruit growing regions has been high. However, the productivity of the fruit remains low; an indicator of low technical efficiency. Using a semi-structured questionnaire, cross sectional data from 123 randomly selected passion fruit producers was used in the study to assess factors that contribute to purple passion fruit production efficiency in the Kenyan highlands. The study established a mean technical efficiency of 58.66%. Orchard age, credit amount used, non-passion fruit income and County variables significantly and positively influenced TE at 5% level. The level of education, extension advice use frequency and market access positively and significantly influenced technical efficiency at 10% level. In order to amend the current efficiency status upwards, passion fruit producers and support institutions should incorporate innovative measures towards resource use efficiency for increased productivity.

Phenotypic characterization of selected Kenyan purple and yellow passion fruit genotypes based on morpho-agronomic descriptors

Phenotypic characterization is crucial in determination of variability of hybrid varieties and their parents. The objective of this study was to determine phenotypic variation among known genotypes of both parent and KPF hybrids, as well as genotypes collected mainly from Embu County which is one of the growing areas of hybrid varieties developed by KALRO. Analysis was done using Minitab 17.0 software. Six out of seven morpho-agronomic descriptors evaluated, showed significant differences among the genotypes under study. A dendrogram based on the 7 morpho-agronomic descriptors discriminated the genotypes into two main clusters with one main cluster (II) carrying only 2 genotypes. Principal component analysis corroborated the findings of the dendrogram, distantly placing the two genotypes further from the other genotypes.

Good Orchard Maintenance and Agronomic Practices as Working Components in Management of Dieback Disease on Passion Fruit (Passiflora sp.) in Kenya.

Passion fruit is of high economic importance in Kenya. In the recent past, diseases have led to decline in fruit production. This study aimed at identifying disease management practices that could be adopted to mitigate disease impacts. Passion fruit varieties used include purple passion (Passiflora edulis Sims) and the KPF hybrid. Field maintenance practices assessed include frequency of orchard sanitation through regular weeding and pruning, pesticide application, nutrient and water provision to plants during the dry season. Agronomic factors assessed include grafting, prunning and effect of wounding in increasing plants’ susceptibility to dieback infections. Assessments were done on-farm and on station; 3 research sites were identified in the field and 1 site was set up on-station. For each of the 3 on-farm sites, a farmer’s performance in orchard maintenance was rated for all the factors on a score of 1-5 and compared to disease severity (1-5 dieback scale ) and incidence (0-100%). Experiments were set up to assess role of grafting on 4 months Original Research Article Annual Research & Review in Biology, 4(9): 1397-1405, 2014 1398 old purple passion seedlings, while effects of prunning and wounding were assessed on 9 months old passion fruit plants of both varieties. Disease establishment was observed and severity was assessed based on the 1-5 dieback scoring chart. Results showed that proper field maintenance reduced disease incidence and severity (12% and 1.6, respectively) in site 1, while poor maintenance yielded higher levels (55% and 4.0, respectively) in site 3. Agronomic practices important in transmission of dieback pathogens on the purple variety were pruning, grafting and wounding. These were found to enhance disease establishment and severity (P ≤ 0.05) on the purple variety while KPF 12 was tolerant to dieback infections. The study established that proper agronomy and field maintenance practices are important and should be integral in control of dieback disease.