Abstract
The objective of the present work was to use MAS in self-pollinated cassava populations for obtaining individuals with high inbreeding (f) aimed at rapid development of partial inbred lines. Three progenies (F0222, F1378 and F1662) were self-pollinated, generating a total of 233 S1 individuals. The progenies and the S1 individuals were evaluated in the seedlings and clonal evaluation trials (CETs). In the CET, plants were evaluated for the following traits: plant height (PH), root dry matter content (DMC), above ground yield (AGY), root (RY) and starch yield (SY). Twenty-seven microsatellites and five minisatellites were used to determine the level of inbreeding of the S1 individuals. Inbreeding (f) values varied from 0.15 to 0.89 within progenies, whereas most of the S1 individuals presented f values above 0.50. In average, 25% of the S1 individuals were selected, which resulted in a 38% inbreeding increase in the cassava progenies. In contrast, phenotypic selection showed no differences in inbreeding increase. Furthermore, there was no correlation between the level of inbreeding and agronomic traits. MAS was efficient for the identification and selection of cassava S1 individuals, with higher inbreeding values contributing to the decrease in the breeding cycles necessary to obtain new cassava inbred lines.
Highlights
Cassava is one of the main sources of carbohydrates for millions of people, mainly in Africa, Asia and Latin America, being the second most important source of starch in the world, just behind maize (Ceballos et al 2015)
Considering only one self-pollination cycle, it was possible to identify S1 individuals with inbreeding coefficients above the expected mean (f > 0.70). This result is of utmost importance to accelerate the development of cassava partial inbred lines, since, after using only a few molecular markers, the results demonstrated the efficiency of marker assisted selection (MAS) for identifying the most homozygous individuals within S1 segregant populations
As for the agronomic traits, the results obtained in this study show associations of medium to high magnitude, especially between RY × starch yield (SY), RY × above ground yield (AGY), AGY × SY and plant height (PH) × AGY
Summary
Cassava is one of the main sources of carbohydrates for millions of people, mainly in Africa, Asia and Latin America, being the second most important source of starch in the world, just behind maize (Ceballos et al 2015). Even though there is great market demand, few improved genotypes are available that meet the growing demands for varieties with high agronomic performance. This possibly occurs due to the relatively short period of the cassava domestication for use as large-scale commercial crops as well as to the most diverse environmental constraints to which the crop is submitted, which means that there is a selection of varieties adapted to specific environments or traits. Cassava breeding programs are relatively recent (beginning in the 1960’s), and there are reports of root yield gains, there is a constant demand for the development of new and highly productive varieties associated with different starch characteristics
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