INTERGENOTYPIC COMPETITION DURING EVALUATION OF MAIZE PROGENIES UNDERLIMITED AND ADEQUATE N SUPPLY

The effects of competition may disguise the true value of progenies in practical maize breeding nurseries, where large numbers of progenies are evaluated in small plots. These effects may be exacerbated where g rowth factors limit performance. Intergenotypic competition among 72 r andomly selected maize (Zea mays L.) S-1 progenies was examined when g rown in non-bordered 1- and 2-row plots and in self-bordered Crow plot s, each at limited N (0 kg ha(-1) applied) and adequate N (200 kg ha(- 1) applied). The same randomization plan was used for each comparison. Traits examined were anthesis date, plant height, ear-leaf chlorophyl l concentration, number of green leaves below the ear at two dates dur ing grain filling, leaf disease (Exserohilum turcicum) score, and grai n yield. Significant correlations between the difference of progeny pe rformance in non- versus self-bordered plots and mean performance of a djacent plots were detected, indicating the presence of intergenotypic competition under both N levels. Changes in rank that occurred betwee n progenies grown in non- versus self-bordered plots did not, however, lead to statistically significant progeny X plot-size interactions. W ith limited N supply, the residual variance of progenies when grown in the smaller non-bordered plots was usually less than when grown in th e larger, self-bordered plots, indicating that soil heterogeneity was probably the main source of residual variance in that trial. Generally , intergenotypic competition explained less than 10% of the difference in performance of progenies in non- versus self-bordered plots. It is concluded that statistical procedures and additional bordering, which would reduce the effects of intergenotypic competition, would only ma rginally improve selection efficiency in progeny trials, and that unde r most conditions the extra expenditure on seed and land that these en tail would not be justified.