The Economic Impact in Developing Countries of ... - AgEcon Search

origins or pedigrees are selected for crosses. In thebreeding nursery, plants are subjected to heavydisease pressure for chosen rust pathotypes, andplants with low to moderate final disease severity areselected. Other morphological markers are also usedin selecting plants. Promising advanced lines aretested at multiple locations to select various types ofdisease resistance and to assess the effectiveness andstability of resistance across environments. Thisinvolves shuttling the segregating populationsbetween sites in Mexico, or between Mexico and “hotspot” locations outside the country. Genetic analysesare conducted for the most important advanced lines.This selection strategy has resulted in thedevelopment of high-yielding wheat lines containingfour to five minor, additive genes and very highresistance levels. Losses from leaf rust in these linesare considered negligible, even under high diseasepressure (Singh et al. 2000).Objective and Scope of the StudyThe objective of this study is to estimate the economicimpact on developing country wheat production ofCIMMYT’s efforts since 1973 to develop leaf rustresistant spring bread wheat varieties. The yields lostby varieties of different resistance categories werecompared to the yields that would have been lost hadthe varieties been fully susceptible. The economicvalue of the wheat yield saved was then calculated.The scope of this study and definition of terms areexplained below.The study encompassed all leaf rust resistancemechanisms carried by CIMMYT-related spring breadwheat. Though CIMMYT emphasizes selection forrace-nonspecific leaf rust resistance (Rajaram et al.1996), a time lag exists between the distribution of anadvanced wheat line and the release of a varietyselected from it by a national program. Breeders insome countries may prioritize other characteristics. Atime period also passes until a variety attains itsadoption ceiling and gradually ceases to be grown infarmers’ fields. Producers often continue to growvarieties with resistance levels that wheat scientistsmay no longer consider satisfactory. CIMMYT-relatedvarieties with race-specific and race-nonspecificresistance can therefore be found in farmers’ wheatfields today.This study deals with developing countries, givenCIMMYT’s mandate to breed advanced lines for thenational agricultural research programs in thosecountries. We focus on spring bread wheat, thoughwinter and facultative habit wheat and durum wheatare included in CIMMYT’s breeding efforts and arealso grown in the study area. However, spring breadwheat covers about two-thirds of the wheat area inthe developing world and comprised an estimated71.5 million hectares in 1997 (Heisey et al. 2002).The analysis is conducted by wheat “megaenvironment”(ME), a classification developed byCIMMYT to guide its germplasm enhancementactivities (Rajaram et al. 1995; van Ginkel et al. 2000).Six MEs have been defined for spring bread wheat(Appendix A). As outlined in the appendix, wefocused on the MEs where spring bread wheat isgrown at low latitudes—that is, MEs 1, 2, 3, 4a, 4b, 4c,and 5. Mega-environment 1 accounts for 36 millionhectares and 54% of the study area of 66.5 millionhectares (Appendix A, Table A1).The term “CIMMYT-related” includes those materialsselected from advanced CIMMYT lines by wheatbreeders in national agricultural research programs.The varieties included are generally descendants ofthe first semidwarf wheat varieties released duringthe late 1960s. These first semidwarfs initially spreadthroughout the irrigated zones most favorable towheat production. Later, more widely adapteddescendants of these varieties spread into lessfavorable growing environments, including rainfedareas with relatively modest production potential.The development and diffusion of these materials isaccomplished through multilocation testing and theexchange of germplasm between CIMMYT andnational programs. CIMMYT sends nurseries,consisting of dozens to hundreds of advanced lines, topartners that request them for testing and selectioneach year (Fox and Skovmand 1996). From thesematerials, local scientists choose lines demonstratingthe best adaptation to local conditions, select fromthem, or cross them to elite local germplasm, andsubmit the resulting materials to national trials. Werefer to the varieties then released as “CIMMYTrelated.”CIMMYT and CIMMYT-related germplasm play animportant role in developing country wheatproduction. Almost 80% of the spring bread wheatarea in developing countries was sown to CIMMYTrelatedsemidwarf varieties in 1997 (Heisey et al.1999). Wheat breeders in these countries indicatedthat materials from CIMMYT International Nurseriesare the most frequently crossed in pursuit of diseaseresistance goals (Rejesus et al. 1997). Most CIMMYTbread wheat germplasm, and several of the majorwheat varieties grown in the developing world,contain in their pedigrees the ancestral source of thegene combinations believed to confer durable rust9