LLAVALLOL, ARGENTINA
Instituto Fitotecnico de Santa Catalina
Universidad Nacional de la Plata and CIGEN (CONICET-CIC-UNLP)

Evaluation and analysis of heat unit requirements for silking in waxy and quality protein maize inbreds developed in Argentina

— Corcuera, VR; Naranjo, CA

During four running growing seasons (2000–01 to 2003–04) in Llavallol (35°S, 58°W), the heat unit requirements for 50% silking (R1 stage, Hanway scale) were evaluated in a group of 19 elite inbreds. The number of days to 50% silking was also evaluated during the same period. These inbreds were developed since 1990 within the frame of a maize quality breeding programme, using the classic method developed by Schull (continuous selfing and conducting ear-to-row). According to the nature of their endosperm, the materials considered may be classified as Waxy, High Quality Protein (QPM) and Waxy and High Quality Protein or Double Recessive (DR). The inbreds tested were sown each year (during the second half of October) in a complete randomized-blocks design with three replicates. The experimental unit or plot was a single row of 5.5 m length. Sowing density used was 71,500 plants/ha. The heat unit requirements of GDD were calculated according to the formula USWB corrected by 2.0°C, as follows:

USWB2.0: [tb + {30 − (tmax. − 30) × 2.0}]/2 − 10

For all the genotypes tested we have considered, tb = 10.0°C. All the measurements and calculations were done on the basis of individual plants. GDDs and number of days for silking required for each of the inbreds studied during the four years may be seen in Table 1. The average is 610.3 ± 9.79°C if all the genotypes are considered. An ANOVA test points to highly significant differences among inbreds (F18-54  = 1.54; p = 0.01). Significant differences due to interanual climatic variations were also found (F3-54 = 12.52; p = 0.01). When GDD or HUR averages were obtained for each inbred after four years, where compared by a least significant differences test (LSD), three groups of homogeneity (D = 102.6; Q54-19  = 5.24; p = 0.05) were detected (see Table 2). The inbreds tested according to their GDDs may be classified as: i) Intermediate: 636.4°C to 656.3°C and 59 to 62 days; ii) Precocious: 586.7°C to 631.8°C and 55 to 59 days; iii) Very precocious: 464.7°C to 578.5°C and 51 to 54 days. According to the t test (Student), significant differences (p = 0.05) were found amongst Waxy, QPM and DR inbreds. It is important to remark here that GDD values for 2003–04 were higher than during the previous years, due to uncommonly low temperatures occurring during the vegetative phase period. Moreover, it was possible to develop a new high quality grain and precocious elite germplasm that will be soon available for commercial use.

Table 1: Heat Unit Requirements for silking in each inbred during four years running

*: Between parenthesis, number of days
**: lost parcel estimated by Allan & Wiskard, modified by Yates.

Table 2: Average HUR estimated for each inbred tested

*: Average values followed by the same letters do not differ significantly at 5% probability (DMS)

Table 3: HUR average values for each group of inbreds tested in Llavallol

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