Competition between cultivated rice (Oryza sativa L.) and the wild rice (Oryza punctata Kotschy ex Steud) in Kenya

Abstract

Rice is an important staple food for more than SO% of the world's population. Kenya rice production comes from cultivated rice (Oryza. Sativa L.) that meets 60% of rice demand. Cultivated rice in the coastal region of Kenya grows in competition with wild rice particularly, Oryza punctata Kotschy ex Steud This study examined the effect of competition on the growth performance from germination to maturity of cultivated (0. sativa) and wild (0. punctata) rice species. Two null hypotheses were formulated; (1) grown together or grown separately, 0. sativa and 0. punctata have the same germination rate, and (2) grown together or grown separately, 0. sativa and 0. punctata have the same growth performance. The study was carried out at Chiromo campus, University of Nairobi. Randomized complete block design with three replications of each treatment was used. Four treatments were used namely; 0. sativa grown alone, 0. sativa grown together with 0. punctata, O. punctata grown alone and 0. punctata grown together with 0. sativa. Data were collected on; seed dormancy, germination rate, stem height, tillering ability, flowering rate, flag leaf area, leaf area index and above and below-ground dry mass. Data were analyzed using the statistical program SPSS version 14. Analysis of variance was carried out at S% significance level. Means separation was carried out by use of Student Newman-Keul's test. The growth curves for stem height and tiller number were found by regression using the least squares method. O. sativa (Basmati 370) had low seed dormancy that was easily broken by water treatment while 0. punctata had high dormancy which was broken by completely dehusking the seeds. The two species were then germinated at 30°C. O. sativa grown together with O~punctata attained a mean germination rate of 7 seeds per day, which was significantly (p<0.001) higher than 6 seeds per day when planted alone. O. punctata grown together with 0. sativa attained mean germination rate of 4 seeds per day, --.,: which was not significantly (P>O.OS) different from 3 seeds per day when planted alone. For both species, the seeds from the mixture attained higher germinatiogs, than the monocultures. 0. sativa was found to be a better performer than O. punctata in relation to ge~ination. There was a significant (P« O.OS) difference among the four treatments in relation to stem height, with mean heights as 84.20±2.07cm for 0. sativa grown alone, 79.39±2.S7cm for O. sativa grown together with 0. punctata, 116.00±13.63cm for O. punctata grown alone and 98.93±8.30cm for 0. punctata grown together with O. sativa. 0. sativa matured within 12Sdays while 0. punctata mat~ed within 108days. O. punctata produced significantly (p<0.001) more tillers than O. sativa whether grown alone or grown together with O. sativa. The mean (±SE) of the number of tillers per hill were 4.43±0.16 for O. sativa grown alone, 4.34"±O.21 for O. sativa grown together with 0. punctata, 9.07±1.82 for 0. punctata grown alone and S.74±2.09 for O. punctata grown together with O. sativa. Competition, therefore, significantly (p<0.001) lowered tiller production within each species. Whether grown together or grown separately, O. punctata flowered 21days earlier than 0. sativa. The mean number (±SE) of the flowering tillers were; 1.30±O.05 for 0. punctata grown alone, O.99±O.04 for 0. punctata grown together with O. sativa, O.54±O.03 for 0. sativa grown alone and 0.49±O.03 for O. sativa grown together with o. punctata. Competition, therefore, significantly (P<O.OOl) lowered the flowering rate of the two species. The monocultures attained significantly (P<O.OOl) higher flag leaf area compared to the mixtures. The mean flag leaf area (±SE) attained by each treatment were; 35.00±O.67 for O. sativa grown alone, 32.50±O.72 for O. sativa grown together with o. punctata, 26.1O±O.67 for 0. punctata grown alone and 24.70±O.55 for O. punctata grown together with O. sativa. Competition, therefore, significantly (p<O.OOl) lowered the flag leaf area of the two species. O. sativa attained significantly (p<O.OOl)higher leaf area index than 0. punctata whether grown alone or grown together. The indexes obtained for each treatment were; O.16±O.01 for 0. punctata grown alone, O.15±O.Ol for O. punctata grown together with O. sativa, O.22±O.Ol for 0. sativa grown alone and 0.21±O.Ol for O. sativa grown together with 0. punctata. O. sativa in monoculture attained an above-ground plant dry mass mean of 1O.98±O.50g that was significantly (P<O.OOl) higher than 9.69±O.50g from the mixture. Likewise, 0. punctata grown alone attained an above-ground dry mass mean of 16.68±O.50g that was significantly (p<O.OOl) higher compared to 13.55±O.50g for 0. punctata grown together with 0. sativa. O. sativa grown alone attained a below-ground plant dry mass mean of 6.68±O.33g that was higher than 6.09±O.33g when growri together with 0. punctata but the difference was not significant (p>O.05). O. punctata grown alone attained a below-ground dry mass meanof 1O.82±O.33g that was significantly (P<O.OOl)higher compared to 8.93±O.33g when grown together with O. sativa. Competition, therefore, significantly (p<O.OOl) lowered the below-ground plant dry mass for 0. punctata but did not have a significant (p>O.OOl) effect on that of 0. sativa. 0. sativa had better overall germination performance thanO:-"punctata in both monoculture and mixture. However, O. punctata attained an overall better growth performance in relation to the studied growth parameters. O. punctata was, therefore, considered a better competitor than O. sativa. Growing the two ~pecies together significantly (P<O.OOl) promoted the germination of O. sativa, but had no significant (p>O.05) effect on O. punctata. Competition significantly (p<O.OOl) lowered the growth performance of the two species. The two null hypotheses of same germination rate and same growth performance for the two species were therefore rejected. For better growth performance, the two species should be grown separately. Future studies should focus on effect of competition pressure on germination, effect of species density on competition and comparison of the nutritional value of the two species, O~sativa and O. punctata.