Evaluation of a Sugarcane (Saccharum spp.) Hybrid F1 Population Phenotypic Diversity and Construction of a Rapid Sucrose Yield Estimation Model for Breeding

Abstract

Sugarcane is the major sugar-producing crop worldwide, and hybrid F₁ populations are the primary populations used in breeding. Challenged by the sugarcane genome's complexity and the sucrose yield's quantitative nature, phenotypic selection is still the most commonly used approach for high-sucrose yield sugarcane breeding. In this study, a hybrid F₁ population containing 135 hybrids was constructed and evaluated for 11 traits (sucrose yield (SY) and its related traits) in a randomized complete-block design during two consecutive growing seasons. The results revealed that all the traits exhibited distinct variation, with the coefficient of variation (CV) ranging from 0.09 to 0.35, the Shannon-Wiener diversity index (H') ranging between 2.64 and 2.98, and the broad-sense heritability ranging from 0.75 to 0.84. Correlation analysis revealed complex correlations between the traits, with 30 trait pairs being significantly correlated. Eight traits, including stalk number (SN), stalk diameter (SD), internode length (IL), stalk height (SH), stalk weight (SW), Brix (B), sucrose content (SC), and yield (Y), were significantly positively correlated with sucrose yield (SY). Cluster analysis based on the 11 traits divided the 135 F₁ hybrids into three groups, with 55 hybrids in Group I, 69 hybrids in Group II, and 11 hybrids in Group III. The principal component analysis indicated that the values of the first four major components' vectors were greater than 1 and the cumulative contribution rate reached 80.93%. Based on the main component values of all samples, 24 F₁ genotypes had greater values than the high-yielding parent 'ROC22' and were selected for the next breeding stage. A rapid sucrose yield estimation equation was established using four easily measured sucrose yield-related traits through multivariable linear stepwise regression. The model was subsequently confirmed using 26 sugarcane cultivars and 24 F₁ hybrids. This study concludes that the sugarcane F₁ population holds great genetic diversity in sucrose yield-related traits. The sucrose yield estimation model, ySY=2.01xSN+8.32xSD+0.79xB+3.44xSH-47.64, can aid to breed sugarcane varieties with high sucrose yield.

Keywords: F1 population; phenotypic diversity; sucrose yield estimated model; sugarcane.

Figure 1

Distribution and correlation analysis of the eleven traits in the hybrid F₁ population. TR, ETR, SN, SD, IL, SH, B, SW, SC, Y, and SY are the abbreviations of tillering ratio, effective tillering ratio, stalk number, stalk diameter, internode length, stalk height, Brix, stalk weight, sucrose content, yield, and sucrose yield, respectively. For each trait, the frequency distribution (bottom), distribution fitting curve (diagonal), boxplot (right), scatter plot (below diagonal), and correlation coefficient between pairs of traits are shown. *, ** and *** represent significant at p < 0.05, p < 0.01, and p < 0.001, respectively.

Figure 2

Cluster tree of the sugarcane F₁ population based on the 11 phenotypic traits. The cluster tree was generated using the standardized traits data through the Ward method. The heatmap of traits was built using the standardized data. TR, ETR, SN, SD, IL, SH, B, SW, SC, Y, and SY are the abbreviations of tillering ratio, effective tillering ratio, stalk number, stalk diameter, internode length, stalk height, Brix, stalk weight, sucrose content, yield, and sucrose yield, respectively. The 135 F₁ genotypes were divided into 3 groups (Group I-Group III), and the groups are indicated by green, blue, and red lines, respectively.

Figure 3

Principal component analysis of the sugarcane hybrid F₁ population. The plot was drawn using the first two PCs of the F₁ population. The red, green, and blue dots indicate the F₁ progenies clustered in Group I, Group II, and Group III, respectively.

Figure 4

Distribution of the estimated and measured sucrose yield of 14 sugarcane cultivars from 2018 to 2020 and 12 cultivars from 2019 to 2021. 2018-E, 2019-E, 2020-E, and 2021-E represent the estimated sucrose yield, while 2018-M, 2019-M, 2020-M and 2021-M represent the measured sucrose yield in the field.

Figure 5

Comparison of the measured and estimated mean sucrose yield of 26 sugarcane cultivars in three crop seasons, including the plant cane, the first ratoon cane, and the second ratoon cane. Mean-E and Mean-M indicate the estimated and measured mean sucrose yield. The sucrose yield of 14 cultivars were measured from 2018 to 2020 in (A), and the sucrose yield of the other 12 cultivars were measured from 2019 to 2021 in (B). “ab” represent significant differences at p < 0.05, and “aa” represent no significant differences at p < 0.05.

Figure 6

Comparison of the measured mean sucrose yield and estimated sucrose yield distribution trends of 24 F₁ genotypes. E and M indicate the estimated and measured mean sucrose yield. The estimated sucrose yield of 24 F₁ genotypes were calculated using the measured stalk height (SH), stalk diameter (SD), stalk number (SN), and Brix (B) of seedling plant.