SEASON OF HARVEST OF AMARANTHUS CRUENTUS L. IN RELATION TO SEED-BORNE MYCOFLORA AND MAJOR SHOOT DISEASES

Abstract

The quality of Amaranthus cruentus L. seeds were influenced both by seasons of harvest and varietal type. The wetness that accompanied harvests of the first (April-June) and second (August-October) seasons greatly-reduced the quality of seeds of cultivars. Quality reduction were in the form of seed malformation,-discolouration and mycelial growth on them. Fifteen fungal species were found to be associated with seeds of the cultivars used. There was a seasonal variability in the occurrence, distribution and the quantity of the seed-borne fungi. Least number and mean percentage seed infection were recorded for NHAC(100) while NHAC(30) and NHAC(33) carried the highest percentage inoculum on the seed testa. Three of the seed-borne fungi were highly pathogenic on seedlings of two of the cultivars while two of the fungi were seed transmitted. Six of these seed-borne mycoflora are new records on Amaranthus seeds in Nigeria. For the two year trials, significantly (p=0.05) least incidence (0%) of dieback, stem blight (8%) were recorded during the first season for NHAC(33) and NHAC(30) while 4% mean leaf blight was obtained from NHAC(100) in the third (December-February) season. Least mean percentage leaf blight was recorded for all the cultivars also by the third season. Conversely, the second season recorded the highest incidence of all these aerial symptoms of the disease caused by Choanephora cucurbitarum (Berk & Rav.) Thaxt. in all the cultivars. Hot water treatment of infected seeds of all cultivars at 60°C for 6 to 8 minutes completely disinfested them of the seed-borne fungi with consequent increase (>95%) in seedling emergence. Also soaking in or dusting of infected seeds with a mixture of Benlate-Captafol or single Captafol at 10g a.i./kg seed controlled the seed-borne fungi. Pre-harvest sprays of Benlate-Captafol mixture or Captafol at 3.3 kg/ha controlled inflorescence infection and seed-borne fungi with resultant yield increases and seedling emergence over the non-treated control.