Increasing cassava planting material through optimizing propagation substrates for cassava minisetts and spacing of field planted tissue derived plantlets

Abstract

Cassava (Manihot esculenta) is a major staple food crop for over 800 million people in sub-Saharan Africa and other parts of the world yet its productivity is still low. This has been attributed to the devastating Cassava mosaic and Cassava brown streak diseases which accumulate in the stems that are used as planting material. Tissue culture coupled with virus indexing has been used for production of clean planting material. However, maximum benefit from tissue culture multiplication of clean planting material has been limited by the low survival rate of cassava tissue culture plantlets experienced at hardening and weaning in the screenhouses. This bottleneck was partly circumvented by use of the minisett technique which was further used to multiply the plantlets that survived. However, appropriate propagation substrate needed to be established for quicker growth of minisetts under screen house conditions. Furthermore, cassava tissue culture derived plants had hitherto not been evaluated in terms of spacing and other agronomic practices under field conditions for production of planting material (stakes) and roots. This study was aimed at determining appropriate propagation substrate combinations and spacing options for optimal production of quality cassava planting material both in the screenhouse and in the field using three cassava genotypes (NASE 03, NASE 14 and NAROCASS 1). Completely randomized design and Randomized complete block design with a 7x3 and 4x3 factorial treatment structures, respectively, were used in the study. Mixing vermiculite, cow manure, lake sand and forest soil in a ratio of 1:1:1:2 (T5) performed better in all parameters than all other treatments followed by the control (cow manure, lake sand and forest soil mixed in ratio of (1:1:2). NASE 14 minisetts grown under propagation substrate vermiculite, cow manure and lake sand and forest soil in a ratio of 1:1:1:2 had the highest number of minisetts (7) and biomass (1.70 g).There was no significant difference (P>0.05) in the amount of biomass produced in T1,T2, T3 and T4 in the three cassava genotypes. Among the four spacing options (100x100cm, 100x50cm, 100x75cm and 75x75cm), NASE 14 under the spacing of 75x75cm obtained the highest amount of stakes (777,483 per hectare) followed by the spacing of 100x50cm. The least number of stakes (231,333) was obtained under NASE 3 grown in the spacing of 100x100 cm in the study. Therefore, for rapid production of planting material in screen house, the best propagation substrate combinations was T5 (1 vermiculite: 1 cow manure: 1 lake sand: 2 forest topsoil) followed by T0 (cow manure, lake sand and forest soil mixed in ratio of 1:1:2) and the best spacing option was 75 x 75cm followed by 100 x 50cm.