Diversity of nematodes on banana (Musa spp.) in Kenya linked to altitude and with a focus on the pathogenicity of Pratylenchus goodeyi

Summary Bananas (Musa spp.) are considered the most important fruit crop in Kenya, grown mostly by smallholder farmers. However, in the past two decades production has declined and has largely been attributed to plant pathogens, including plant-parasitic nematodes. To assess the understanding and awareness that banana farmers have of nematodes, a survey was conducted. The incidence, abundance and distribution of nematodes in relation to altitude were determined for different banana types on 180 farms and the pathogenicity of Pratylenchus goodeyi, originating from three different altitudinal locations, was compared on two banana cultivars. Just 2.3% of farmers were aware of nematode damage and symptoms, none of whom applied any management measures. The highest abundance of nematodes was recorded at an altitude range of 1601-2000 m a.s.l., with Pratylenchus, Meloidogyne and Helicotylenchus being the predominant genera. Across all altitudinal locations, cooking banana had higher densities of nematodes than dessert bananas. In pots, P. goodeyi populations from Embu (1300 m a.s.l.) appeared more aggressive and with higher levels of multiplication than the population from Oyugis (1100 m a.s.l.). Cooking banana (‘Ng’ombe’) was more susceptible than dessert banana (‘Sukari Ndizi’). Nematode damage is more prominent in areas at higher altitude and on cooking banana cultivars. The findings provide key information in guiding informed and suitable management decision thresholds in relation to potential climate change.

Root Endophytism by Pochonia chlamydosporia Affects Defense-Gene Expression in Leaves of Monocot and Dicot Hosts under Multiple Biotic Interactions

A study was carried out on the effect of the root endophytic fungus Pochonia chlamydosporia on plant systemic signal of defense related genes during fungal or nematode parasitism. Different biotic stress factors were examined, inoculating roots of dicot and monocot hosts with the endophyte, and measuring the expression of defense genes in leaves. A first greenhouse assay was carried out on expression of PAL, PIN II, PR1 and LOX D in leaves of tomato cv Tondino inoculated with Phytophthora infestans (CBS 120920), inoculating or not the roots of infected plants with P. chlamydosporia DSM 26985. In a second assay, plants of banana (Musa acuminata cv Grand Naine) were artificially infected with Fusarium oxysporum f. sp. cubense Tropical race 4 (TR4) and inoculated or not with DSM 26985. In a further experiment, banana plants were inoculated or not with P. chlamydosporia plus juveniles of the root knot nematode (RKN) Meloidogyne incognita. A similar assay was also carried out in vitro with adults and juveniles of the lesion nematode Pratylenchus goodeyi. Differential expression of the defense genes examined was observed for all plant-stress associations, indicative of early, upward systemic signals induced by the endophyte. Changes in expression profiles included a 5-fold down-regulation of PIN II at 2 dai in leaves of tomato plants treated with P. infestans and/or P. chlamydosporia, and the up-regulation of PAL by the endophyte alone, at 2 and 7 dai. In the TR4 assay, PR1 was significantly up-regulated at 7 dai in banana leaves, but only in the P. chlamydosporia treated plants. At 10 dai, PIN II expression was significantly higher in leaves of plants inoculated only with TR4. The banana-RKN assay showed a PR1 expression significantly higher than controls at 4 and 7 dai in plants inoculated with P. chlamydosporia alone, and a down-regulation at 4 dai in leaves of plants also inoculated with RKN, with a PR1 differential up-regulation at 10 dai. Pratylenchus goodeyi down-regulated PIN at 21 dai, with or without the endophyte, as well as PAL but only in presence of P. chlamydosporia. When inoculated alone, the endophyte up-regulated PR1 and LOX. The gene expression patterns observed in leaves suggest specific and time-dependent relationships linking host plants and P. chlamydosporia in presence of biotic stress factors, functional to a systemic, although complex, activation of defense genes.

The Ethiopian staple food crop enset (Ensete ventricosum) assessed for the first time for resistance against the root-lesion nematode Pratylenchus goodeyi

Summary Pratylenchus goodeyi appears to be the most prevalent nematode pest of enset in Ethiopia, where it can occur in extremely high densities. However, the damage to yield or how different enset cultivars react to the nematode has yet to be determined. The current study therefore sought to establish a first assessment of these reactions by enset to P. goodeyi infection. Determining pest-resistant cultivars is an important task in developing management strategies. Our study evaluated nine enset cultivars to establish host response and identify potential sources of resistance. In addition, the pathogenicity of P. goodeyi was assessed on three enset cultivars. After 9 months’ growth, significant differences in final population densities (Pf) and reproduction factor (RF) were observed amongst the nine cultivars, with ‘Gefetanuwa’ the most susceptible (Pf = 25 799 and RF = 12.9), and similarly in a repeat experiment for 4.5 months (Pf = 126 534 and RF = 63.3). ‘Maziya’ and ‘Heila’ were the most resistant in the first experiment (Pf < 455 and RF < 0.2) as well as in the repeat, together with ‘Kellisa’ (Pf < 5255 and RF < 2.6). In the pathogenicity experiment four inoculum densities significantly affected the Pf and RF but not among the three cultivars ‘Maziya’, ‘Arkiya’ and ‘Heila’. This is the first known study to assess genotype reaction to P. goodeyi, which shows that there are significant differences in the reactions of different cultivars and that resistance appears to be present in enset.

Pratylenchus goodeyi. [Distribution map].

A new distribution map is provided for Pratylenchus goodeyi Sher & Allen. Secernentea: Tylenchida: Hoplolaimidae. Hosts: Musa spp. Information is given on the geographical distribution in Europe (Greece, Crete, Portugal, Madeira, Spain, Canary Islands), Asia (China, Hainan, Kazakhstan, Pakistan), Africa (Burundi, Cameroon, Congo Democratic Republic, Ethiopia, Kenya, Rwanda, Tanzania, Uganda), North America (Mexico, USA, California), Oceania (Australia, New South Wales, Queensland).

In vitro evaluation of nematicidal properties of Solanum sisymbriifolium and S. nigrum extracts on Pratylenchus goodeyi

The root-lesion nematode, Pratylenchus goodeyi, is among the most economically damaging parasites of banana plants. Nematode control can benefit from searching for novel bio-nematicides. The present study was carried out to assess the potential nematicidal properties of two Solanum species (Solanum sisymbriifolium and S. nigrum) against P. goodeyi, using dichloromethane, acetone, ethanol and either cold or hot water extracts of the plants. Water extracts of both plants at a concentration of 10 mg ml−1 greatly affected nematode movement and also caused mortality. The analysis of sequential extracts at the same experimental concentrations showed that, although water extracts affect nematode mobility and mortality, the acetone extract from S. nigrum was the most efficient, causing 100% mortality after 23 h exposure. The results showed that S. sisymbriifolium and S. nigrum extracts contain chemical components that induce morphological changes in the body structure of the root-lesion nematode, affect mobility and cause mortality. The nematostatic and nematicidal potential of the extracts described herein merit further studies to find novel bio-nematicides against the root-lesion nematode.

Potential biological control of lesion nematodes on banana using Kenyan strains of endophytic Fusarium oxysporum

The root-lesion nematode Pratylenchus goodeyi is a common pest of banana in Kenya, which results in significant yield losses. An emerging option for the management of banana nematodes includes the use of endophytic fungi, which cause no damage to their hosts but often extend benefits, such as enhanced protection against various biotic and abiotic constraints. In the current study, non-pathogenic Fusarium oxysporum strains originating from banana (Musa spp.) in Kenya (4MOC321 and 11SR23) and Uganda (V5w2) were evaluated for their efficacy against P. goodeyi in tissue culture-derived plantlets (cv. Giant Cavendish and cv. Grand Nain) in pots. Pratylenchus goodeyi densities were 47-60% lower in endophyte-inoculated relative to non-inoculated plants and root necrosis damage was reduced by >30%. Endophyte treatment had no effect on plant growth parameters compared with untreated control plants. The performance of the two Kenyan strains was equally effective as the positive control (V5w2), thus demonstrating their potential as nematode bio-control agents under Kenyan growing conditions.