Melhoramento genético de abóbora tipo Tetsukabuto: desempenho agronômico, diversidade genética e tolerância a viroses

Abstract

The objective was to evaluate agronomic performance and identify the best experimental Tetsukabuto pumpkin hybrids; evaluate the genetic diversity between these hybrids; and select progenies for growth habit and tolerance to Zucchini yellow mosaic virus (ZYMV) and Squash mosaic virus (SqMV), aiming to promote genetic variability for the formation of germplasm. In the first experiment, 21 interspecific experimental hybrids and four controls (Nara, Takayama, Kanda and Jabras), which were pollinated by the cultivar 'Samantha' and 'Moranga Exposição'. Thevariables evaluated were total and commercial fruit productivity (PTF and PCF), average mass of total and commercial fruit (MMFT and MMFC), number of total and commercial fruits (NFT and NFC), thickness of the pulp and skin (EP and EC), diameter of the internal cavity of the fruit (DCI), height of the fruit (AF), fruit diameter (DF), soluble solids content (TSS), colorimetric parameters L*C*h of the skin and pulp, skin texture (TC), pulp moisture (UP), fruit shape (FF), fruit size (TF), fruit uniformity (UF), white belly (BB) and skin and pulp color (CC and CP). The best unbiased linear prediction (BLUP) was estimated using restricted maximum residual likelihood (REML) and cluster analysis (UPGMA method) and principal component analysis (PCA) were performed. For the second experiment, seeds from the first segregating generation (PS1) of the five best hybrids selected in the first trial (HE-07, HE-12, HE-16, HE-18 and HE-35) were used. Seedlings from each segregating population were produced and the viruses were inoculated separately. The individuals were evaluated using rating scales regarding the incidence of viruses from the molting stage to the field production stage. Individuals with symptom s were eliminated and the remainder, no symptoms, were identified according to their growth habit (long branch, bush or semi-bush) and crossed with the cultivar ‘Samantha’, originating the segregating population of the second crossing (PS2). The fruits obtained were agronomically evaluated. These data were analyzed descriptively, in addition to UPGMA and PCA analysis. In the first experiment, the hybrids showed significant differences for the characteristics MMFT, MMFC, EP, AF, TSS, TC, FF, TF, UF, BB and CC, with emphasis on HE-05, HE-07, HE-12 and HE-14, which surpassed the controls and presented excellent potential for launch on the market and/or incorporation into new improvement programs. There was genetic divergence among the 25 hybrids, with the formation of four distinct groups, with the group of hybrids HE-01, HE-12, HE-14, HE-22 and Takayama standing out in MMFT, MMFC, AF and FF. In the second experiment, considering viable and inoculated seedlings from the segregating population until the field phase, 4.06% showed tolerance to the ZYMV virus and 4.65% to the SqMV virus. Viable fruits and seeds were obtained from 19 individuals tolerant to ZYMV and 25 individuals tolerant to SqMV. Three dissimilar groups were formed for ZYMV and four for SqMV. It was concluded that PS2 seeds, tolerant to both viruses, (I7PS1HE-07ZYMV, I4PS1HE-12ZYMV, I1PS1HE-18ZYMV, I5PS1HE-35ZYMV, I11PS1HE-35ZYMV, I35PS1HE-35ZYMV, I42PS1HE-35ZYMV, I18PS1HE-35S qMV, I20PS1HE-35SqMV , I6PS1HE-07SqMV, I17PS1HE-35SqMV, I21PS1HE-35SqMV, I21PS1HE-18SqMV, I7PS1HE-35SqMV and I10PS1HE-35SqMV) will be advanced in the genetic improvement program, requiring the introduction of the Bu gene in individuals tolerant to SqMV.