Manihoti
Cassava (Manihot esculenta) is globally the fourth most important staple crop after rice, wheat and maize, and features prominently in the diet of millions of people throughout the tropics. Grown on >18 million ha worldwide, cassava cultivation sustains the livelihoods of countless smallholder farmers, many of whom operate in degraded environments. In South and SE Asia alone, cassava is grown by >8 million farmers and is the engine of the rural economy in countries such as Cambodia and Laos. In Indonesia, cassava continues to be a key source of calories for humans and domestic animals, and a food security crop for poorer and rural segments of the local population, while it steadily gains ground as a cash crop in countries such as Vietnam and Laos.
Up till 2008, Asian cassava experienced a virtual absence of pests and diseases. However, recent appearance of different (exotic) mealybug species means that farmers abruptly had to account for a complex of destructive pests. In 2008, the cassava mealybug Phenacoccus manihoti was reported from Thailand and has since spread to Laos, Vietnam, Cambodia and Indonesia. At the start of the project, little was known about the distribution, impact, ecology and management of the invasive cassava mealybug in Asia.
Mealybug damage is a recent phenomenon in Asia, and biological control appears to be the most feasible and effective solution. Cassava appears to rely on both direct and indirect tactics to ward off its principal insect pests. Cassava plants produce extra-floral nectar (e.g., petiole exudate) that is readily consumed by natural enemies, and boost their fitness and pest control efficacy.
Microbes enhancing plant growth and affecting multitrophic interactions
Plant growth promotion was the first beneficial effect known for the symbiosis of plants with mycorrhiza and nitrogen-fixing bacteria, whereas knowledge on such phenomena related to plant growth promoting rhizobacteria (PGPR), root endophytic fungi and plant growth-promoting fungi (PGPF) has emerged more recently . Beneficial effects on plant growth have a high relevance for agricultural ecosystems because they reduce the need for fertilisers, leading to a decrease in pollution of agricultural soils and water. For instance, Trichoderma spp. are PGPF that are commercially available and are widely used in agriculture. Both chewing insects and phloem feeders benefit from the higher content of nitrogen and other limiting nutrients in plant tissues and phloem sap, respectively. Surprisingly, to date, no studies appear to have analysed the effect of beneficial soil-borne microbes on phloem sap composition.
Dips, inoculants, and soil amendments
Since the arrival of P. manihoti, cassava growers in Thailand have come to embrace the use of systemic insecticides such as neonicitinoids, thereby further reducing an already slim margin of profits and income. Thus far, control of mealybugs in Southeast Asia has relied on stake treatments with a range of synthetic neonicitinoid chemicals.
Fungal soil inoculants have the potential to affect bottom-up regulatory processes and the multitrophic interactions. These include several commercially available agents such as Isaria fumosoroseus, Metarhizium anisopliae, Beauveria bassiana, and several mycorrhizal species. Most of these have not been tested for their potential direct or indirect impacts on cassava-feeding insects, and none for higher trophic levels (parasitoids, predators).
Indonesia has listed 4000 organisations with the title and the rights of universities. Being one of the most populous countries on the globe, future problems in connection with food and feed have to be solved at the grass roots level. Part of the project has been conducted together with the Universitas Hassannuddin, Makassar, South Sulawesi. The cooperation within the “World Class Professorship Programme” is highlighted and described under “World Class Professorship Programme”.
