Cytologic and histologic symptoms of beet yellows

Abstract

The sugar beet ( Beta vulgaris L.) and New Zealand spinach ( Tetragonia expansa Murr.) infected with the virus of beet-yellows disease develop characteristic inclusions. As seen with the light microscope these inclusions appear granular-alveolate, or fibrous, or composed of a series of parallel bands, possibly arranged spirally. The inclusions may be spherical, or ovoid, or much elongated. They may occur singly or in variable numbers in a given cell. The inclusions occur most consistently in the phloem tissue, specifically in parenchyma and companion cells. They occur also in various ground tissues outside the phloem and in the epidermis. They may be present in the phloem in the absence of any other symptom. Phloem necrosis is another typical symptom and consists in the death of companion cells, some parenchyma cells, and of sieve elements. The external symptoms in the affected sugar beet are correlated with various abnormalities in the mesophyll and vein parenchyma: hypertrophy, hypoplasia, destruction of chloroplasts, and necrosis.