Comparative biology and growth behaviour of Pennisetum polystachyon(L.) Shult. and P. pedicellatum Trin.

Abstract

Pennisetum polystachyon (L.) Shult. and P. pedicellatum Trin. are two major grass weeds that are widespread in young plantation crops and non-arable areas of the tropics. The present investigation was undertaken to have an understanding on the biology, growth behaviour and fodder production potential of these two Pennisetum spp. at the Research F~ College of Horticulture, Vellanikkara during 1998-2000. Germination tests were conducted at monthly intervals. P. polystachyon did not show any dormancy and started germination as soon as the seeds are collected (December). P. pedicel/alum seeds remained dormant during December and January and it started germination by February only. Both species showed above 80 per cent germination by late March. Germination percentage started to decline in P. polystachyon after April. Phenological characters of both species were noted from a natural population during the year 1999. Seeds of Pennisetum spp. started germination soon after the receipt of monsoon showers by the end of April. Flowering started after the completion of the rainy period in September. Plants started senescence by mid December in P. polystachyon and mid November in P. pedicellatum. Both Pennisetum species studied showed remarkable regeneration ability from different cutting heights. The percentage of plants regenerated was similar in both species. Allelopathic reactions of roots, leaves and seeds were also studied. Boiled and unboiled extracts were prepared and germination test were conducted using cowpea, bhindi and cucumber as test crops. The cold and boiled leaf extracts of both species did not show any effect on germination of test crops. However, cold root extract of both Pennisetum spp. reduced the germination percentge ofbhindi. Cold root extract of both species also showed some promotery effect on shoot length in cowpea. Seed extracts showed inhibitory effects only on cowpea germination. Growth was comparatively fast in P. pedicellatum than P. po/ystachyon during its early stages. P. polystachyon showed higher leaf : stem ratio than P. pedicellatum. Growth indices like LAR, LWR, RGR, AGR and NAR were similar in both Pennisetum spp. In terms of total green fodder production, P. pedicellatum was superior to P. polystachyon. Two cuttings, one at 70 days after sowing and the other just before flowering recorded maximum fresh weight of fodder. Though crude protein content was similar in both the species, P. pedicellatum showed a higher crude fibre content than P. polystachyon. The results indicate that as the fodder quality is good, utilizing these grasses as cattle feed can be one of the strategies for managing them. However, cultivation of these grasses for fodder purposes involves some risks because of their high reproductive capacity and persistence.