Response of Photosynthetic Pigments and Yield of Pinto Bean (Phaseolus vulgaris L.) to Weed Management Methods

Abstract

IntroductionBean is one of the most important legumes worldwide for direct human consumption and it is a rich source of protein and carbohydrates. Bean is weak in competing with weeds due to its slow growth during the early stages. Therefore, competition with weeds causes a significant reduction in grain yield at the end of the growing season. Weeds and crops are always competing for obtaining nutrients, water, light and space. Weed competition is a kind of nonliving stress, which effect on plant yield. The photosynthetic capacity of plants depends on abiotic factors such as the quality and quantity of light. Each of the photosynthetic pigments such as chlorophyll a, b and carotenoids absorb light at a different wave length. The rate of photosynthesis and biomass production in plants is also largely dependent on the chlorophyll content of leaves. The weed interference in the plant growth maybe caused a change in the content of carotenoids and chlorophyll pigments in plant leaves. Pinto bean (Phaseolus vulgaris L.) cultivars, with different morphological and genetic characteristics, show different responses in the presence of weeds, which may ultimately result in possible difference in yield. Measurement of growth indices is necessary to study the competitive ability of species during the growth period. Materials and MethodsIn order to investigate the effect of different chemical and non-chemical weed control managements on the yield of determinate and indeterminate bean varieties, an experiment was conducted as factorial based on a randomized complete block design with three replications. This field experiment was carried out in Behshahr, Mazandaran, in 2021. The first factor was different weed control methods: application of trifluralin herbicide as pre-sowing 2.5 liters per hectare; application of trifluralin herbicide 2.5 liters per hectare + one weeding; wheat mulch in the amount of two tons per hectare; application of bentazon 50% of the recommended dose; application of bentazon 75% of the recommended dose; application of bentazon 100% of the recommended dose; weed-free control and control with weed infestation and the second factor includes bean cultivars: Negin variety (determinate growth type) and Sadri variety (indeterminate growth type). Weeds were sampled at flowering and final harvesting stages, and weed species, density, and dry weight of weeds were measured. Also, photosynthetic pigments and yield were investigated. Results and DiscussionThe results showed that weed species in the field were from 9 plant families and included 10 species. From the total species observed in the field, 4 species have C4 photosynthetic pathway, 4 species have C3 photosynthetic pathway and one species has CAM photosynthetic pathway. The Amaranthus retroflexus L. and Portulaca oleracea L. species had the highest frequency and Chrozophora tinctoria and Physalis alkekengi had the lowest frequency in the field. In all three stages (21 days after planting, flowering and final harvesting stages), the highest density and dry weight of weeds were observed in the control treatment without weeding, and among the weed management treatments, mulch and bentazon 100% treatments caused a decrement in the density and dry weight of weeds in both Negin and Sadri cultivars. Based on the results, the highest chlorophyll a, b and total chlorophyll were observed in both Negin and Sadri cultivars in the weed-free control treatment, and the lowest values were in the control treatment without weeding. Also, the control treatment without weeding had the highest amount of carotenoids in Negin cultivar (0.41 mg.g-1 fresh weight) and in Sadri cultivar (0.37 mg.g-1 fresh weight), while the lowest ones in Negin and Sadri cultivar (0.29 and 0.28 mg.g-1 fresh weight, respectively) was observed in the weed-free control treatment. The highest seed yield of Negin and Sadri cultivar (1957.11 and 2426.01 kg.ha-1, respectively) were observed in the weed-free control treatment. ConclusionsIn general, it can be concluded that the Sadri cultivar with higher competitive ability has performed better against the weed than the Negin cultivar. Among the weed management treatments, the non-chemical management of mulch and the chemical treatment of bentazon 100% had better performance.

Keywords

• bentazon
• chlorophyll
• competition
• mulch