Estimating peach palm fruit surface area using allometric relationships

Abstract

Fruit surface area is an important trait in studies of developmental physiology, as well as in entomological and phytopathological research, where damage caused by insects and/or microorganisms needs to be quantified. Nonetheless, direct measurement of this trait is difficult, not very precise and destructive. This study establishes allometric relationships to estimate the surface area of peach palm (Bactris gasipaes Kunth, Palmae) fruits. Five fruits were harvested, at different maturation stages, from each of 18 plants. Image digitalization and edition methodology was adapted and compared with the traditional gravimetric method. Regression analysis and curve fitting were used to compare the two methods and establish allometric relationships among fruit surface area and fruit weight and size. The method based on image digitalization was twice as fast as the gravimetric method. Curve fitting for all pairs of independent and dependent variables was better with the image method. For most relationships, the best model was the exponential function (Y = ax b ), although, due to its simplicity, the linear model is also adequated. The best allometric estimates of fruit surface area (Y) were obtained using the product of fruit length by maximum width (x) were: Y = 2.077 x 1.189 (R 2 = 94.8%); and Y = -6.261 + 3.961 x (R 2 = 94.5%). Traits needed to establish this relationship are easily measured and non-destructive in nature. Validation of the allometric equations is essential when applied to other populations or landraces. Key words: Bactris gasipaes, pejibaye, area estimation, curve fitting ESTIMATIVA DA ÁREA SUPERFICIAL DE FRUTOS DE PUPUNHEIRA POR RELAÇÕES ALOMÉTRICASRESUMO: A área superficial do fruto é de importância fundamental em estudos relacionados à fisiologia do desenvolvimento, bem como em pesquisas entomológicas e fitopatológicas, onde o dano causado por insetos e/ou microorganismos precisa ser quantificado. No entanto, a medição direta dessa característica é difícil, além de não muito precisa e destrutiva. Neste estudo foram estabelecidas relações alométricas visando estimar a área superficial de frutos de pupunheira (Bactris gasipaes Kunth). Foram colhidos cinco frutos por planta, em diferentes estádios de maturação, de 18 plantas matrizes. A metodologia baseada em digitalização e edição de imagens foi adequada ao presente estudo e comparada com o método gravimétrico. Com base em análise de regressão e ajuste de curvas, os dois métodos foram comparados, determinando-se ainda relações alométricas entre área superficial e peso e dimensões do fruto. O método de digitalização de imagens mostrou-se duas vezes mais rápido que o gravimétrico, obtendo-se bom ajuste para todos os pares testados. Para a maioria das relações estabelecidas o modelo de melhor ajuste foi a potência da variável independente (Y = ax b ). No entanto, pela simplicidade, recomenda-se também o modelo linear. Para a variável (x) obtida pela multiplicação do comprimento e largura máxima do fruto, as equações que permitiram estimar a ...

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