ETIOLOGY OF ONION (ALLIUM FISTULOSUM L.) WHITE TIP AT THE FARM TESORITO, MANIZALES-CALDAS

Abstract

The onion´s white tip is an endemic disease at the Tesoritos´ farm of the Universidad de Caldas, whose causal agent is unknown, therefore, this research was conducted, seeking through a series of treatments, to discard as sumptions that exist about the cause of the disease, such as nutritional deficiencies and damage by plant parasite nematodes. This study was conducted at the Universidad de Caldas, under a hydroponic system. Five doses of boron were used: 0,5 1,0 20 40 and 60 ppm in a completely block design, with five repetition and six seedlings per repetition. It was determined disease incidence, height of seedlings and dry weigh of roots and foliage. It was found a direct relation between boron (B) concentration and disease incidence and inverse in relation to seedlings´ height and dry weigh of both roots and foliage. It was demonstrated that the white tip of onion is caused by excess of B, which induces chlorosis and apical deformation of the leaves, followed by weakness and death of the leaves, typical symptoms of the disease.