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Despite cassava’s significance as a staple crop in tropical and subtropical regions, there is limited understanding of how specific environmental factors influence the productivity of different cassava varieties. This study investigated the complex relationship between environmental factors and cassava yield traits such as fresh root yield (FRY), dry root yield (DRY), starch content (SC) and harvest index (HI) using data obtained from six cassava varieties cultivated for five seasons (2014 to 2019) across nine major locations in Thailand. A total of 41 distinct environmental trials were conducted, representing a range of conditions encompassing various rainfall and temperature patterns, as well as soil characteristics. Field experiments were conducted using a randomized complete block design with four replicates at each location. Climatic data, including air temperature and precipitation, along with soil parameters, were recorded and analyzed to assess their impact on cassava yield traits. Regression analysis revealed distinct coefficients for environmental factors affecting different yield parameters. Cumulative precipitation during 4-5 months after planting (MAP) and 6-10 MAP, as well as the average air temperature during 2-3 MAP and 6-10 MAP, positively influenced cassava yield. However, negative correlations were observed between soil organic matter and HI. Furthermore, the average air temperature at 4-5 MAP, 6-10 MAP, and 1-10 MAP negatively impacts FRY and DRY, while cumulative precipitation during 1 MAP and 2-3 MAP negatively impacts the HI and SC traits. Varieties exhibited varied responses to environmental factors, emphasizing the need to consider specific variety responses for accurate interpretation. The study introduces a novel approach for selecting specific cassava genotypes adapted to distinct environmental conditions by grouping regression coefficients across evaluated parameters. These findings provide insights for optimizing agricultural practices to enhance cassava productivity and contribute to sustainable crop cultivation.

The gene pools for breeding cassava (Manihot esculenta Crantz) in Africa currently contain only a fraction of the existing genetic variation found in Latin America where the crop originates. Our research aimed to broaden the genetic base in Africa by introducing Latin American (LA) germplasm. The first set of introductions comprised sexual seeds that led to the evaluation of 20,032 seedlings in Nigeria between 1990 and 1994. A second set comprised in vitro cultures, where the dominant CMD2 gene for cassava mosaic disease (CMD) resistance was introgressed into LA germplasm through marker‐assisted selection (MAS). Through MAS 156 genotypes were preselected for the gene and evaluated in Nigeria between 2004 and 2006. Initial results from the first set of introductions indicated that LA germplasm was highly susceptible to CMD, minimizing its usefulness in African cassava‐breeding programs. In the second set of introductions from LA, introgression of the CMD2 gene resulted in high CMD resistance under African field conditions. Now at advanced stages in the African breeding program, 14 genotypes combining CMD resistance and high yield are being evaluated. Marker‐assisted introgression of CMD resistance into LA germplasm has improved the potential value of LA germplasm for Africa and enhanced the prospect of elite LA genotypes being released as improved varieties in Africa.

Evaluations with a uniform plant stand are fundamental for efficient selections in cassava (Manihot esculenta Crantz) breeding. However, it is difficult to correct data of missing plants. The overall objective of this study was to analyze yield losses in agronomic trials and to develop a function that satisfactorily adjusts plot yields affected by a varying number of missing plants. Eight clones were initially evaluated in different locations for five consecutive years. For every genotype, mean plot yields decreased as the number of missing plants increased. Average losses ranged from 10.6 to 78.8% by removing from one to eight plants, respectively. Yields per plant increased significantly when more than four plants were removed due to a compensatory growth effect. Graphic analyses showed that the power function was the best explaining the relationship between fresh root yield and number of harvested plants. A model that properly adjusted yield for all varieties but one is proposed. Hopefully, this formula to adjust yields will help to improve the quality of cassava trials worldwide.

Cassava (Manihot esculenta) breeding at the earlier stages so far has been mainly based on a mass phenotypic recurrent selection, as little data is taken. This has resulted in a long breeding cycle and lack of organised information on the breeding values of parental lines used in the breeding programmes. The International Institute of Tropical Agriculture (CIAT) recently initiated a scheme to try and correct this, by introduction of replication and blocking in the clonal evaluation trial (CET) and collection of data on all genotypes at early stages of breeding. The aim of the study was to evaluate a CET using the new breeding scheme. Replicating and blocking of clones improved the accuracy of the data obtained. High broad-sense heritability values, comparable to those at advanced selection stages, were obtained, as environmental effects were minimised. The highest was for harvest index (HI) (0.80), followed by cassava frogskin disease (CFSD) (0.79), dry matter content (DMC) (0.75) fresh and dry root yields (DRY) (0.73), root weight (RtWt) (0.61), number of commercial roots (0.60) and roots per plant (RtPlt) (0.43). DMC, HI and RtWt were identified as important variables in selection and determination of economic yield at early stages of selection.