Cassava (Manihot esculenta) occupies a uniquely important position as a food security crop for smallholder farmers in ares of the tropics where climate, soils, or societal stresses constrain production. Given its reliability and productivity, cassava is the most important locally produced food in a third of the world's low-income, food-deficit countries. It is the fourth most important source of carbohydrates for human consumption in the tropics, after rice, sugar, and maize. World production of cassava from 1994-1996 averaged 166 million tons/year grown on 16.6 million hectares (ha), for an average yield of 9.9 tons/ha. Approximately 57% is used for human consumption, 32% for animal feed and industrial purposes, and 11% is waste. Africa accounts for 51.3% of the production; Asia, 29.4%; and Latin America, 19.3%. The area planted to cassava in Africa, Asia, and Latin America is 10.3, 3.7, and 2.6 million ha, respectively.

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This paper discusses the: cassava arthropod complex; crop damage and yield loss; major pests (i.e. mites, mealybugs, whiteflies, Lepidoptera, stemborers, burrower bugs, lacebugs), bioecology damage and management; secondary pests; and trends in pest management (i.e. pesticides, cultural practices, biological control and host plant resistance).

Insect pests and plant diseases reduce cassava yields substantially, posing a threat to food security throughout the developing world. While agricultural scientists have recognized these threats, few assessments of the geographic distribution of cassava pests and diseases have been made at the global scale. The goal of this study is to make such an evaluation for four key biotic constraints to cassava production in developing countries: whiteflies, cassava green mites, cassava mosaic disease and cassava brown streak disease. Occurrence records were obtained from laboratory and biodiversity databases and from the scientific literature. These records were then used in ecological niche models to predict the potential distribution of cassava pests and diseases. The distribution maps were cross validated by holding back 20% of the occurrence records. Potential distribution maps were developed by combining the results of the best ecological niche models. Hotspots for potential cassava pest and disease outbreaks include the Mato Grosso in Brazil, northern South America, the African rift valley, the southern tip of India and much of Southeast Asia, where all four biotic constraints show high potential suitability. Our work highlights how potential geographical shifts in infestation hotspots for several cassava biotic constraints will require intensified monitoring, evaluation and research to prevent yield losses and ensure food security.

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can produce in degraded soils, and offers resistance to its most important diseases and pests. It is naturally Cassava (Manihot esculenta Crantz) is an important commodity tolerant to acidic soils and offers the convenient flexibilfor industrial processes in tropical countries as one of the few alternaity to be harvested when the farmers need it. Cassava tives to compete with imported maize (Zea mays L.). To maintain has benefited by technological inputs in the area of this competitiveness, cassava breeding needs to be as efficient as possible. This study provides one of the first attempts to produce breeding (Kawano et al., 1998;Kawano, 2003) to sucquantitative genetic data to aid breeding efficiency, through the analycessfully satisfy the needs of farmers and processors. sis of a diallel set among nine parental clones adapted to the midalti-The general scheme for cassava breeding is indeed a tude valleys environment. Thirty clones represented each F 1 cross phenotypic masal selection. Large numbers of segregat-(with three exceptions). Evaluations were conducted in two coning genotypes is evaluated in a lengthy process that retrasting environments with three replications in each location. The quires as many as 6 yr for completion (Jennings and specific combining ability (SCA) effects were relatively more impor-Iglesias, 2002). Individual genotypes (clones) are setant than general combining ability (GCA) effects for root yield. In lected and then multiplied to take advantage of the the case of harvest index, dry matter content (DMC) and plant type vegetative propagation of the crop. architecture GCA effects were about twice as large as those from Little progress in understanding the inheritance of SCA effects. Reaction to mites (Mononychellus tanajoa Bondar) and white flies (Aleurotrachelus socialis Bondar) (based on single-Aé reo 6713, Cali, Colombia. H. Ceballos, also Univ. Nacional de from these 30 plants were obtained. Minor selection was un-Colombia, Carrera 32, Chapinero vía Candelaria, Palmira, Colombia. avoidable at this stage based on the capacity of the botanical Received 21 May 2004. Crop Breeding, Genetics & Cytology. *Correseeds to produce vigorous seedlings and plants capable of sponding author (h.ceballos@cgiar.org).producing six good quality vegetative cuttings.

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