Abstract
ABSTRACT The objective of this work was to estimate and compare phenotypic and genetic parameters after three cycles of intrapopulation recurrent selection for fresh corn grown under three nutrient availability conditions. Three experiments derived from the same population (MV-003) were conducted to assess the ability of progenies to absorb nutrients, one under adequate fertilization (control; MV-006), one under low nitrogen availability (N; MV-006N), and one under low phosphorus availability (P; MV-006P). The experiments were carried out in randomized blocks, with 64 half-sib progenies and three replications for each nutritional condition. Chlorophyll index, plant height, ear insertion, ear diameter, ear length, unhusked ear yield, and marketable husked ear were evaluated. The populations showed variability for the three nutrient availability conditions. The variability reduced after only three selection cycles; thus, evaluating a higher number of half-sib progenies, above 64, under low N and P availability is indicated. The rates used to identify the most efficient progenies in breeding programs should be close to the appropriate one, with a slow reduction after the selection cycles. The variability will be thus maintained, with a greater possibility of identifying more promising progenies. In addition, the frequency of favorable alleles increases more gradually and effectively. The N and P rate of 60 kg ha-1 is not indicated as a critical level for the initial phase of the program.
Highlights
Corn is an important crop in Brazil, the midwest region of the country is responsible for the largest planted area, approximately 8,524 thousand hectares and the highest mean yields (6,095 kg ha-1), as in the state of Goiás, which has a mean yield of 6,805 kg ha-1 (CONAB, 2020).Despite the national and state importance of this crop, few corn cultivars intended for fresh consumption are available in Brazil, which makes it impossible for farmers to meet demand and all market niches (RODRIGUES et al, 2018)
The effect of the different nutrient availability was significant for most characteristics (p≤0.05), except for plant height in the control, and ear diameter in the low P availability treatments (Table 2). These results showed phenotypic variability between progenies, denoting the possibility of obtaining genetic gains with selection, even under low nutrient availability
The coefficients of variation (CV) were relatively low for most characteristics, with a mean of 9.2%, except for unhusked ear yield (UEY) and marketable ear yield (MEY), which presented a mean CV of 26.5% (Table 2)
Summary
Corn is an important crop in Brazil, the midwest region of the country is responsible for the largest planted area, approximately 8,524 thousand hectares and the highest mean yields (6,095 kg ha-1), as in the state of Goiás, which has a mean yield of 6,805 kg ha-1 (CONAB, 2020).Despite the national and state importance of this crop, few corn cultivars intended for fresh consumption are available in Brazil, which makes it impossible for farmers to meet demand and all market niches (RODRIGUES et al, 2018). High productivity is linked to soil fertility conditions; the appropriate fertilizer rates vary in the literature according to soil type, crop, management, market niche, and local edaphoclimatic conditions, which affect the plant development; in addition, studies have prioritized proper and sustainable applications (PAIVA et al, 2012). This indicates that seeds should be produced for each specific production condition, considering the technology level adopted, to meet this market demand. Half the applied nitrogen fertilizer is used by the plants in tropical soils, the remainder is lost by volatilization, leaching, or other causes (REPKE et al, 2013)
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