Residual Effects of Moisture Stressed Seedlings in the Nursery on Field Performance of Cacao Genotypes

Abstract

Cacao (Theobroma cacao L.) belongs to the family Sterculiaceae and the genus Theobroma. Recently, with the application of molecular marker, cacao was reclassified to the family Malvaceae (Alvensonet al., 1999). Cocoa (Theobromacacao L.) is an evergreen tropical lowland tree crop, native to the rainforest regions of Central and South America and indeed West Africa, which became the major producer from the mid-1960s (Opeke, 2006). There are over twenty species in the genus but Theobromacacao is the only one cultivated widely (Opeke, 2006). It is a cash crop of international significance, and has been a major source of foreign exchange for producing countries. Cacao is highly valued for its seeds – the cocoa beans. West Africa is a dominant cocoa producing region, because of its suitable soil and favourable climatic conditions. Abstract: An experiment was conducted at the Teaching and Research Farm, Federal University of Technology, Akure, in the rainforest zone of South-West Nigeria, to examine the residual effects of moisture stress of seedlings in the nursery on field performance of cacao genotypes. The experimental materials were two cacao genotypes (Amelonado and F3 Amazon) and two improved lines (PA 150/34 and PA 150/36) which were obtained from Cocoa Research Institute of Nigeria (CRIN), Ibadan. The seeds of the genotypes were sown in nursery pots, and seedlings were subjected to varying levels (0.6, 0.9 and 1.5 litres) of watering in the nursery. After ten (10) months in the nursery, the differentially watered seedlings were transplanted on the field in June, 2017. The experiment was laid out in a 4 x 3 factorial combination arranged in a Split Plot Design at three replicates per treatment. The cacao genotypes constituted the main plot while the differentially watered seedlings the sub-plot treatment. Data were collected on plant height (cm), stem girth (mm), number of leaves, and number of branches, number of dead seedlings and number of seedlings bearing dead twigs/branches and final survival count at end of dry season. Results showed that the effects of cacao genotypes anddifferential watering of seedlings in the nursery were significant on the measured growth and development variables of cacao on the field. The development of leaves and solar radiation properties (incidence and transmitted radiation) within cacao canopy varied during the course of the year among treatments. Across the differentially watered seedlings, highest radiation transmission within canopy was obtained between January and April. The ratio of transmitted to incident radiation were lowest for 1.5 l watered seedlings and lowest for moderate (0.9 l) and severe water stressed (0.6 l) seedlings. The effect of cacao genotype was pronounced on the time dynamics of canopy development (number of leaves and leaf area index), compared with F3 Amazon and the improved cacao varieties (the PA series), Amelonado had best leaf development across the measurement dates. Lowest number of leaves per plant were found for period between 360 – 90 DOY and highest between 150270 DOY (the dry and rainy season periods respectively. Within measurement periods, lowest LAI and highest PAR were observed at DOY 90 (February of a year) while highest LAI and lowest PAR between 180 and 360 DOY (between June and December of a year). The effect of differential watering was pronounced on seedling mortality on the field during the year, and lowest number of dead trees per treatment was obtained for the 1.5 l watered seedlings and highest for 0.6 l. Highest number of trees bearing dead twigs/branches were observed during the dry season (360-90 DOY, December to March of a year) and lowest between 120 to 300 DOY (April to October). The survivability of seedlings on the field was high (75 %) irrespective of treatment received in the screen house. It is concluded that the effects of pre-field (nursery) water stress of seedling was profound on field performance of cacao genotypes.