Kernel quality, evolutive cycle length and yield of waxy, high protein quality and double recessive inbreds developed in Argentina

--Corcuera, VR, Bernatené, EA, Naranjo, CA

During 1990, a maize quality breeding programme was initiated at the Instituto Fitotecnico de Santa Catalina aimed at obtaining high quality protein, waxy and double recessive hybrids capable of being used for human and animal nutrition, as well as new staples for several industries. Amongst other traits, evolutive cycle length was measured in the foundational materials, backcrosses, inbreds and different types of hybrids derived from them, through Heat Unit Requirements (HUR) and number of days to mid silking (R1 stage according to Hanway scale). In this paper, we present briefly the results obtained for evolutive cycle length to R1, yield and chemical nature of the endosperm of fifteen inbreds developed at the Institute and evaluated in field trials at Llavallol (35 ºS, 58 ºW) during three consecutive growing seasons (2000/1, 2001/2 and 2002/3). The materials were arranged in a 3 replicate complete randomised block design. Each plot consisted of a single row of 5.5 m, sown at a density of 71,500 plants/ha. The chemical composition and density of the grains was measured using a NIR device model Isotec 1227. Heat unit requirements in each inbred were measured on the basis of the individual plant, according to the USWB method corrected by 2.0 °C as follows:

USWB_2,0 = {t _min + [30 - ( t_max - 30) x 2.0]} / 2 - 10

t_min: minimum temperature (10 °C)
t_max: maximum temperature

Number of days to mid-silking were also evaluated for each genotype. Yield was measured considering kernel weight/ear (15% humidity), number of ears per plant and number of plants/ha.

Most of the waxy maize used as foundationals in 1990 were precocious (418–518 °C for silking), whilst the foundational high quality protein maize showed a long evolutive cycle (780–870 °C for silking). Although inbreeding tends to lengthen evolutive cycle, it was possible to obtain through selection amongst and within families, short or medium evolutive cycle, high quality protein (472–676 °C, 47 to 64 days) and waxy maize inbreds (505–681 °C, 48 to 65 days). On the other hand, whether double recessive inbreds (high quality protein and modified starch) showed short or medium evolutive cycle length, some denoted a long one (490–715 °C, 51 to 68 days), (see Table 1 and Table 2).

In general terms, selection by precocity associated to quality breeding was successful, and unpublished data from a single hybrid field trial evaluated in Llavallol during the growing season 2002/3 showed that the evolutive cycle length of these was dominated by the most precocious parent of the cross.

The yield of the inbreds studied ranges from 1,430 kg/ha to 7,722 kg/ha, with an average of 4,891 kg/ha. If the genotypes are grouped according to the nature of their endosperm, the average yields are 4,962 kg/ha (2,502 to 6,506 kg/ha) for high quality protein inbreds, 3,946 kg/ha (1,430 to 6,077 kg/ha) for waxy inbreds and 5,765 kg/ha (3,932 to 7,722 kg/ha) for double recessive inbreds (see Table 2).

Protein, starch, oil content and density were measured in ten inbreds and data are shown in Table 3. Five inbreds had ≥ 5% oil content, 7 had ≥ 10.5% protein content and 5 had ≥ 70% starch. The highest density values correspond to opaque2 or double recessive genotypes, whilst lower values were observed in waxy inbreds, which is surely related to the chemical compositions of the starch (see Table 3). The correlation analysis showed that only oil content is related to yield (r = 0.49) whilst the correlation index starch-protein was r = -0.59. Considering the yield and the protein content of the inbreds studied, it can be stated that protein yield fluctuates from 149 to 873 kg of protein/ha.

In brief, precocious, high yielding and high kernel quality inbreds could be developed using Schull’s method and conducting the materials ear-per-row during the first inbreeding generations, and later using balanced composites selecting within and amongst families.