Abstract
ABSTRACT Corn kernels or seeds that remain after harvest can germinate and become a troublesome volunteer plant where bean crops are grown. The objective of this study was to evaluate the effect of time of emergence of volunteer corn on growth parameters, photosynthetic pigments and chlorophyll fluorescence in bean plants, competition for soil and light and light resources. The study was conducted in completely randomised experimental design, in 2×2×2+2 factorial scheme with four replications, involving two bean cultivars in competition with volunteer corn, emerging seven days before and simultaneously with beans, besides the partitioning of the competition by soil and light, just light and two controls without competition. We measured the levels of chlorophyll a, b, total and carotenoids, parameters related to chlorophyll fluorescence and bean growth variables. Volunteer corn was more competitive when it emerged seven days before the beans. When competition was established by light resource, there was a reduction in photosynthetic pigments and morphological variables of the bean plants. When competition by soil and light resources occurred, there was a reduction not only in photosynthetic pigments and morphological characteristics, but also in the chlorophyll fluorescence variables. There were significant correlations between the growth variables of the bean plants and chlorophyll fluorescence, which makes it an important analytical tool for quantifying the stress caused by weeds.
Highlights
Beans (Phaseolus vulgaris) are one of the most important food crops in Brazil
Regarding competition for soil and light, there was a reduction in height of bean plants when beans were grown with volunteer corn that had emerged early compared to when beans and corn emerged simultaneously or compared to the controls (Table 1)
Volunteer corn had 39% higher dry biomass compared to corn which simultaneously emerged with bean plants; indicating that bean plants were suppressed in height only when volunteer corn emerged seven days earlier
Summary
Beans (Phaseolus vulgaris) are one of the most important food crops in Brazil. Beans have become an option after cropping with corn in the Southern region of Brazil. Corn kernels or seeds that remain after harvest can germinate and become a troublesome volunteer plant where bean crops are grown. Volunteer corn growing in bean crops can cause yield losses that amount to approximately 20% for each volunteer corn plant per square meter (Sbatella et al, 2016). Volunteer corn has a capacity to germinate at different times in the bean crop, and its time of emergence may alter the competition between it and the crop. Weeds that emerge early show good growth and have an increased effect on yield losses of crops by acquiring advantage to resources of the environment and have a high relative growth rate (Agostinetto et al, 2004). Weeds that emerge after crops usually cause a low level of interference with crop yield (Vandevender et al, 1997)
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