Use of histochemistry, section-to-slide digestion and image analysis for evaluation of digestibility in reed canarygrass (Phalaris arundinacea L.) genotypes

Abstract

A useful tool for both nutritionists and plant breeders would be the development of forage quality selection techniques that are simple, rapid and inexpensive. This study evaluates histochemistry, section-to-slide and image analysis techniques for their usefulness in a forage digestibility evaluation program. Digestibility of stem and leaf material for nine parental genotypes of the reed canarygrass (Phalaris arundinacea L.) cultivar Rival were compared using a gravimetric digestion technique. Based on differences observed for stem digestibility, two low- and two high- digestibility genotypes were selected for further study. The four genotypes were harvested for stem material at three stages of growth. Tissues examined included the epidermis (E), cortex (C), phloem (P), sclerenchyma ring (SR), xylem (X), vascular bundles (VB), and parenchyma (PA). Histochemistry staining, using acid phloroglucinol (AP) or chlorine sulphite (CS), indicated genotype and growth stage differences with all tissues except P and X. However, only the AP staining of the SR and PA, and the C with both stains were similar for the two low-digestibility genotypes. Section-to-slide digestion also indicated genotype and growth stage differences, but did not provide similar values for the two low-digestibility genotypes. Tissue area percentages, determined by image analysis, were different among genotypes for P, SR, and PA. A growth stage effect was observed for SR tissue area. The only tissues with similar area percentages for the two low-digestibility genotypes were the PA and SR. The results indicate potential use for histochemistry and image analysis to determine differences in plant stem digestibility. The SR and PA may be the key tissues involved in digestibility differences among genotypes and growth stages. Key words: Forage, digestibility, microanatomy, histochemistry, section-to-slide, image analysis