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Ninety-eight cassava accessions were grown in augmented randomized complete block design to screen for superior clones with desirable traits. The desirable traits were root number (RTNO), fresh root yield (FYLD), harvest index (HI), dry matter (DM), cyanide potential (CNP), mean plant height (MPHT) and level of branching (LOBR). Three standard varieties were used, namely 30572, 91/01730 and 91/023227. Acessions that were superior to the standard types in more than one trait were 92/0681, 92/02325; 92/0455, 88/02555; Alice Local and 88/02555. These accessions could be selected and put into crossing blocks to combine the traits into one genotype. The present results show that augmented designs are efficient in the identification of superior cassava genotypes with desirable traits. Selection for desirable traits is necessary to enhance cassava breeding in Africa. The initial stages of breeding programmes include field-testing of large numbers of accessions. The tests are laborious, time consuming and need to be repeated to minimize effects of uncontrolled environ- mental factors. With limited resources, the breeder needs to increase efficiency at an early testing in order to reduce the number of clones for uniform trials. Federer (1961), working with sugar cane, proposed the augmented designs as a solution to overcome the problem of having large number of genotypes for field-testing. These designs allow elimination of soil differences as common causes of error in comparison of entries, and can successfully be employed in genetic studies and breeding programmes for crop improvement, being more cost effective than fully replicated trials (Spehar, 1994). These designs are derived from expanded randomized complete blocks in which standard varieties are present in all blocks. The empty spaces of the expanded blocks are filled with the varieties for which information about the performance is needed. The statistical analysis on the standard varieties identifies the varying soil attributes as measured by the blocks, and allows one to correct for these and make a valid comparison. The method has been used in field screening trial of soya bean (Spehar, 1994). The objective of the experiment was to adapt the augmented randomized complete block design to screen cassava germplasm and select superior clones with desirable agronomic traits to facilitate their use in breeding programmes.

Field screening of cassava (<i>Manihot esculenta </i>Crantz) germplasm for desirable traits by the use of augmented design