Identification of high seed oil yield and high oleic acid content in brazilian germplasm of winter squash (Cucurbita moschata D.)

Cucurbita moschata D. seed oil contains approximately 75% unsaturated fatty acids, with high levels of monounsaturated fatty acids and antioxidant compounds such as vitamin E and carotenoid, constituting a promising food in nutritional terms. Associated to this, the Brazilian germplasm of C. moschata exhibits remarkable variability, representing an important source for the genetic breeding of this vegetable and other cucurbits. In this context, the present study evaluated the productivity and profile of the seed oil of 91 C. moschata accessions from different regions of Brazil and maintained in the Vegetable Germplasm Bank of the Federal University of Viçosa (BGH-UFV). A field experiment was conducted between January and July 2016. The tested C. moschata accessions showed high genetic variability in terms of characteristics related to seed oil productivity (SOP), such as the mass of seeds per fruit and productivity of seeds, providing predicted selection gains of 29.39 g and 0.26 t ha-1, respectively. Based on the phenotypic and genotypic correlations, greater SOP can be achieved while maintaining high oleic acid content and low linoleic acid content, providing oil of better nutritional and chemical quality. In variability analysis, the accessions were clustered into five groups, which presented different averages for SOP and fatty acid content of seed oil; approach that will guide the use of appropriate germplasm in programs aimed at genetic breeding for SOP and seed oil profile. Per se analysis identified BGH-4610, BGH-5485A, BGH-6590, BGH-5556A, BGH-5472A, and BGH-5544A as the most promising accessions in terms of SOP, with average (μ+g) of approximately 0.20 t ha-1. The most promising accessions for higher oleic acid content of seed oil were BGH-5456A, BGH-3333A, BGH-5361A, BGH-5472A, BGH-5544A, BGH-5453A, and BGH-1749, with average (μ+g) of approximately 30%, and almost all of these accessions were also the most promising in terms of lower linoleic acid content of seed oil, with average (μ+g) of approximately 45%. Overall, part of the C. moschata accessions evaluated in the present study can serve as a promising resource in genetic breeding programs for SOP and fatty acid profile, aiming at the production of oil with better nutritional and physicochemical quality.

132 where PS is the productivity of seeds (t ha -1 ); NFP is the number of fruits per plant; MSF is the 133 mass of seeds per fruit (g); * 1,111 is the number of plants per hectare; SOC is the oil content 134 expressed as the percentage of the seed mass on a dry basis (%); and SOP is the seed oil 135 productivity (t ha -1 ).

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Initially, the seeds were dried in a forced air circulation oven for 72 h at 30°C. Next, 20 137 g seeds from each genotype were ground in a Willey knife mill with a 1 mm sieve. SOC was 138 determined in an extractor (ANKOM XT15) following extraction with petroleum ether using 139 a standard AOAC method (Thiex et al., 2003). Before loading in the extractor, the ground seed 140 samples were dried in an unventilated oven at 105°C for 2 h. Then, approximately 2 g samples 141 were transferred to filter envelopes (XT4; ANKOM technology), which were sealed and placed 142 in the extractor. Oil was extracted from the samples with ether circulation for 30 min at 90°C, 143 and the percentage of oil was calculated as the difference between the sample weight before 144 and after extraction. SOC was expressed in grams per 100 grams of seeds on a dry basis. 166 represents the vector comprising the effect of blocks (random effect); a represents the vector 167 comprising the effect of accessions (random effect); t represents the vector comprising the 168 control effect (fixed effect); and e represents the error vector. W, X, and Z represent the 169 incidence matrices of parameters b, a, and t, respectively, with the data vector y. All statistical 170 analyses were performed based on the genotypic values.

171
The genetic parameters were obtained based on the following estimators:

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The correlations between characteristics were analyzed based on the following model: where Cov (x, y) represents the genetic covariance between two variables, X and Y, and σ 2 185 and e σ 2 g (y) represent the genetic variances corresponding to the variables X and Y, 186 respectively.

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The significance of correlations was analyzed in GENES (Cruz, 2013)

356
Regarding the fatty acid profile of seed oil, the highest genotypic variance and very 357 high heritability for the content of oleic acid, demonstrate the high genetic variability and 358 feasibility of identifying C. moschata accessions that can produce oil with higher oleic acid 359 content. As a result, the predicted selection gain for oleic acid was 6.99%, which corresponded 360 to the greatest selection gain among the components of seed oil (Table 1). Furthermore, the 361 linoleic acid and PUFA content exhibited high genetic variability, also demonstrating the 362 feasibility of identifying C. moschata accessions that can produce oil with lower linoleic acid 363 content, providing predicted selection gains of -5.12% for this first fatty acid (Table 1).

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The     (Table 2). This clustering is consistent with 445 the high estimates of genotypic variance and heritability for the evaluated characteristics 23 446 related to SOP, including MSF and PS, as well as those related to the fatty acid profile of seed 447 oil, including oleic and linoleic acid content (Table 1)   Based on their highest genotypic averages for SOP, the groups 5 and 2 were identified 499 as the most promising for this characteristic (Table 3). Consistent with this result, per se 500 analysis identified accession BGH-4610 from group 5 as the most promising in terms of SOP, 501 with the (μ+g) estimate of 0.27 t ha -1 (Table 4). In addition, accessions BGH-5485A, BGH-502 6590, BGH-5556A, BGH-5472A, and BGH-5544A from group 2 were also identified as 503 promising in terms of SOP in per se analysis, with the (μ+g) estimate of ~0.20 t ha -1 (Table 4).

504
The groups 3 and 2 were identified as the most promising in terms of SOP with higher 505 oleic acid content (Table 4). Associated with this, the accession BGH-5456A from group 3 was 506 identified as most promising in terms of high oleic acid content in per se analysis, with the 507 (μ+g) estimate of 37.20% (Table 4). The accessions BGH-3333A, BGH-5361A, BGH-5472A, 508 BGH-5544A, and BGH-5453A from group 2 and the accession BGH-1749 from group 3 were 509 also identified as promising in terms of high oleic acid content, with the (μ+g) estimate of 510~30.00% (Table 4). The identification of promising groups and per se identification of 511 accessions with high oleic acid content in the seed oil are associated with the high amplitude 512 of (μ+g) estimates for this characteristic (Figure 4).

513
The groups 3 and 2 also presented the lowest averages for linoleic acid and PUFA 514 content, confirming them as the most promising in terms SOP with lower PUFA content (Table   515 4

571
The tested accessions expressed high genetic variability in terms of MSF and PS, 572 providing the predicted selection gains of 29.39 g and 0.26 ha -1 , respectively.

573
Phenotypic and genotypic correlations indicated that a greater C. moschata SOP can be 574 achieved by selecting for higher PS and MSF. Correlations also indicated that a greater SOP 575 can be obtained while maintaining high oleic fatty acid content and low linoleic acid content, 576 providing oil with better nutritional and chemical quality.

577
In the analysis of variability, the 91 accessions tested in this study were clustered into 578 five groups, allowing the identification of the most promising groups in terms of greater SOP 579 and higher oleic acid content in the oil, an approach that will guide the use of this germplasm 580 in breeding programs aimed at improving the SOP and fatty acid profile.

581
Per se analysis identified the accessions BGH-4610, BGH-5485A, BGH-6590, BGH-582 5556A, BGH-5472A, and BGH-5544A as the most promising in terms of SOP, with the (μ+g) 583 estimate of ~0.20 t ha -1 . Accessions BGH-5456A, BGH-3333A, BGH-5361A, BGH-5472A, 584 BGH-5544A, BGH-5453A, and BGH-1749 were identified as the most promising in terms of 585 higher oleic content in oil were, with the (μ+g) estimate of ~30%, and most of these accessions 586 were also the most promising in terms of lower linoleic acid content in oil, with the (μ+g) 587 estimate ~40%. Therefore, part of the C. moschata germplasm evaluated in the present study 588 is a promising source for the genetic improvement of SOP and fatty acid profile, aiming at the 589 production of oil with better nutritional and physicochemical quality.