Physiological disorders of Potato

Physiological disorders

       There is another group of diseases commonly referred to as non-parasitic diseases which are the result of physiological imbalance caused by unfavourable environmental conditions. These are:

Internal brown spot

        It is characterized by irregular, dry brown spots scattered through the flesh of tubers. These spots are never found in vascular region as in case of brown rot. It is a very minor disorder that appears particularly in light sandy soils which are not irrigated regularly. The affected tubers lose much of their value as table potatoes. It is not transmissible, however, planting of severely affected tubers should be avoided as they often produce weak plants. An old variety, Craigs Defiance, is prone to this.

Black heart

         If potato tubers are stored in air at a temperature of 35°–40°C they develop in a few days, a condition known as ‘black heart’ in which the inner tissues break down and become black. Lack of oxygen is the probable cause. It is also probable that at high storage temperature, accumulation of CO₂ at the centre of the tuber might contribute to damage and to the subsequent decrease in respiration and development of black heart. This is of minor importance as it appears only in ordinary over-heated and ill-ventilated farm stores. Therefore, avoid storage temperature above 35°C and poor ventilation.

Hollow heart

       Hollow heart consists of an irregular cavity in the centre of tubers. In tissue surrounding the cavity, there is no decay or discolouration. Hollow heart condition appears often in varieties which bulk rapidly and produce over-sized tubers. In extra large-sized tubers of Kufri Jyoti and Kufri Sindhuri hollow heart may appear. This condition can be avoided by closer spacing of plants and avoiding excessive use of fertilizers.

Chilling injury

   

           Chilling injury may follow prolonged storage of tubers at temperature of about 0°C. This results in discoloured blotches in the flesh of tubers which vary from light reddish-brown to dark brown, diffuse brownish black patches on skin and reduce or completely inhibit sprouting of affected tubers when planted.

Freezing injury

           Freezing injury occurs as a result of ice formation in potato tubers when exposed to temperatures between –1° and –2°C. Tubers which are only briefly frozen show, when cut in half, a blue-black discontinuous ring in the vascular region. More severe injury leads to blue-black necrotic network in the pith, in addition to necrosis in the vascular region. In tubers frozen for more than half an hour the cut surface of the thawed tuber shows diffuse areas of black discolouration. If the tubers are frozen for about 4–5hr they show no blotch or discolouration but on thawing the whole tuber becomes wet and soft and liquid oozes out of it.