097号 page 117/212

このページは 097号 の電子ブックに掲載されている117ページの概要です。
秒後に電子ブックの対象ページへ移動します。
「電子ブックを開く」をクリックすると今すぐ対象ページへ移動します。

概要：
Recent Adoption and Spatial Diversity of Modern Rice Varieties in the Philippines 107For spatial diversity indicators, we employed three spatial diversity indices usedby ecologists (Benin et al., 2004....

Recent Adoption and Spatial Diversity of Modern Rice Varieties in the Philippines 107For spatial diversity indicators, we employed three spatial diversity indices usedby ecologists (Benin et al., 2004; Smale et al., 2003). Table 1 shows the concepts andmathematical formulae used in deriving the indices adapted from Smale et al. (2003)and applying them in the case of rice.Table 1. Spatial diversity indices usedIndex Concept Mathematicalconstruction Explanation Adaptation in thispaperMargalef Richness D = (S-1)/ln N(D=>0)Number of species (S)recorded, correctedfor the total numberof individuals (N)summed over speciesS is the number ofrice varieties grownin a season by therespondents, N is thetotal hectares of riceplanted by the respondentsin that seasonBerger-ParkerRelativeabundanceor InversedominanceD = 1/(Nmax/N)(D=>1)The more dominantthe most abundantspecies, the lower theindex valueInverse of maximumarea share occupiedby any single ricevarietyShannon Both richnessand relativeabundanceD = -Σpi lnpi(D=>0)The pi is the proportion,or relative abundanceof a speciesThe pi is the area shareoccupied by the ithvarietySource: Magurran (1988) and Smale et al. (2003)2. Results and Discussion1) Adoption rate of newly released varietiesTable 2 shows the trends of varieties planted by variety group. Until 1997, therewas still a significant percentage of farmers planting MV2 varieties which weredesigned to ensure yield stability by incorporating resistance to multiple pests anddiseases. We can, however, see a trend of progression in the use of modern varieties?adecreasing trend in the use of MV2 and increasing use of MV4. From 1992 to 2002,MV3 varieties were widely used. The noted slight increase in the use of TVs wasbrought about by the commercial release of some local traditional varieties which havegood performance and are popular selections among farmers.The proportion of the total area planted with new varieties (varieties released inthe previous 7 years from the time of survey) is on average around 30% to 40% ofthe total rice area in the country (Table 3). In the 1993 DS, for example, 37% of the