Low or excessive soil fertility is a major constraint to potato production. The influence of each individual nutrient element on potato plants under field studies remains ambiguous due to the influence of environmental variations. Creating an in vitro model plant with deficient or excessive nutrient content will provide a more controlled study and allow for a better understanding of how the concentration of one element can affect the uptake of other elements. Here we designed a tissue culture-based nutrition control system to systematically analyze the effects of essential nutrients on potato plants. Insufficient or excessive nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) contents were created by modifying the Murashige and Skoog (MS) medium. Deficient to toxic plant nutrient statuses were successfully defined by the evaluation of dry biomass and morphological symptoms. The results showed that plant shoot growth, nutrient uptake and content, and nutrient interactions were all significantly impacted by the changes in the MS media nutrient concentrations. These tissue culture systems can be successfully used for further investigations of nutrient effects on potato production in response to biotic and abiotic stresses in vitro.

Entomopathogenic fungi are known to control vector mosquito populations. Thus, understanding the infection dynamics of entomopathogenic fungi is crucial for the effective control of insect pests such as mosquitoes. We investigated the dynamics of Beauveria bassiana s.l. 60-2 infection of Anopheles stephensi by exposing the mosquito to fungus-impregnated filter paper through two infection routes and then comparing the mortality and extent of infection. Fungal development was observed after using this inoculation method with both the tarsus route and the proboscis route, but early mosquito death occurred only after infection through the proboscis route. Fungal hyphae invaded almost all the tissues and organs before or after the death of the host, and fungal invasion of the brain was highly correlated with mortality. Moreover, although all mosquitoes that were alive at various time points after inoculation showed no fungal infection in the brain, fungal infection was detected in the brain in all dead mosquitoes. Our results suggest that fungal invasion of the brain represents one of the factors affecting mortality, and that the proboscis route of infection is critical for the early death of vector mosquitoes.

Three parental strains of Lecanicillium spp. and eleven hybrid strains previously obtained by protoplast fusion were evaluated for their virulence to different life stages of Trialeurodes vaporariorum. Egg treatment yielded no statistically significant difference on the hatching rate of eggs as opposed to the mortality of subsequent hatched larvae which was over 80% by 4 hybrid strains and the commercial product Vertalec^®. Among the strains, hybrids 2aF1 (4.6 × 10⁴ conidia/ml) and 2aF43 (5.7 × 10⁴ conidia/ml) showed one order lower concentration of LC₅₀ value compared with Mycotal^® (6.7 × 10⁵ conidia/ml). Mortality of 1st instar larvae infected through direct inoculation and hatched larval mortality through egg inoculation resulted significantly in lower LC₅₀ values in most of the tested strains. In bioassays against 4th instar larvae, Vertalec^® provided the highest mortality (65.2%) with other strains producing mortalities between 11.1% and 43.0%. Four hybrid strains of 2aF4, 2aF30, 2aF43 and 2aF31 produced significantly higher mortality against adults than Mycotal^® and Vertalec^®. Our results demonstrated that many hybrid strains exhibited higher pathogenicity than that displayed by their parental strains, suggesting that protoplast fusion can be useful to produce strains with greater potential for the development of powerful microbial control agents.

The objectives of this study were to evaluate the potential of an orange Malawian local maize variety MW5021 by comparing with a hybrid variety DKC-9089 for nutritional quality and processing properties such as proximate and mineral composition as well as pasting and thermal properties of the flour, and resistance against Prostephanus truncatus infestation during storage of the grain. Maize plants sampled for the experiments were cultivated under three different fertilizer applications, namely 0, 92 and 184 kg-N/ha, considering the chemical fertilizer input among Malawian smallholder farmers. Even without fertilizer input, significantly higher contents of crude protein, Mg, P, Ca, Fe and Zn were observed in MW5021, as compared with DKC-9089. Among pasting properties, setback of the flour slurry from MW5021 was significantly lower than DKC-9089 for all fertilizer treatments. Two-way ANOVA indicated that MW5021 had significantly lower number of grains damaged by P. truncatus than DKC-9089, throughout 12 weeks of storage experiment at 28±2°C. Thus, this study revealed that the Malawian orange local variety MW5021 retained by the smallholder farmers has considerably higher nutritional quality and P. truncatus resistance as well as lower retrogradation hardening after cooking the flour, than the hybrid maize DKC-9089. Key words: Maize, Mineral composition, pasting properties, postharvest losses, Prostephanus truncatus, Malawi.