COMPETITION FOR NODULE SITES BY COWPEABRADYRH1ZOBIUM AND PARASITIC FLOWERING PLANTS AS AFFECTED BY INOCULATION, N, P AND Mo.

COMPETITION FOR NODULE SITES BY COWPEABRADYRH1ZOBIUM AND PARASITIC FLOWERING PLANTS AS AFFECTED BY INOCULATION, N, P AND Mo.

Abstract:

Studies in the greenhouse and field were initiated to evaluate the effects of Striga and Alectra on cowpea nodulation and N-fixation, to determine the influence of cowpea – Bradyrhizobium strains on Striga and Alectra and the influence of phosphorus, molybdenum and nitrogen on Striga and Alectra infection of cowpea. The effect of inoculant strains of cowpea – Brady rhizobium on Striga and Alectra infection of cowpea was studied in the greenhouse. The results showed that inoculation with Brady rhizobium strain IRc 506c resulted in the lowest incidence of infection by these parasitic flowering plants and thus, produced higher total dry matter, nodule number, nodule dry weight and percentage nitrogen fixed than strain IRc 291 or IRc 461a, suggesting that strain IRc 506c is more efficient in competing for nodule sites or in fixing atmospheric nitrogen with the cowpea varieties used. Two field experiments were carried out during the 1995 and 1996 cropping seasons. The first experiment investigated the influence of urea nitrogen fertilizer applied seven days after planting on the incidence of Striga and Alectra infection of cowpea. The second field experiment studied the effect of phosphorus and Mo on Striga and Alectra infection in cowpea. Phosphorus and Mo were applied also at seven DAP. Results of the first field experiment showed that application of 15kgNha-‘ urea nitrogen fertilizer reduced the incidence of Striga and Alectra infection in susceptible varieties (SAMPEA-7, SAMPEA-1 and IT82D-849) but not in the resistant variety (B301) by 16 and 14% (in terms of the number of attached Striga and Alectra per cowpea plant, respectively); and 21 and 19% (in respect of the number of emerged Striga and Alectra per cowpea plant respectively). Among the susceptible varieties, IT82D-849 performed better than SAMPEA-1 and SAMPEA-7. Total cowpea dry matter (TDM) yield was increased by 12% in the fertilized, uninfested plots compared to the control. In the fertilized Striga – or Alectra – infested plots, TDM was increased by 19 or 17%, compared to the unfertilized, infested plots respectively. Grain yield increased with the application of l5kgNha1 by 19% in the fertilized, uninfested plots compared to the control. The Striga or Alectra infested but fertilized plots produced more grain yield than the unfertilized but infested plots by 21 or 10% respectively. Cowpea variety B 301 produced the highest grain yield. Nodulation (nodule number and nodule dry weight) was increased by 8 and 4% in the fertilized uninfested plots compared to the control. On the other hand, plants in the Striga – infested but fertilized plots had 28% higher nodule number and 5% higher nodule dry weight compared to the unfertilized but infested plots. Similarly, plants in Alectra infested but fertilized plots had 19 and 5% higher nodule number and nodule dry weight, than unfertilized plots respectively. Results of the second field experiment indicated that application of 40kgPha-1 in all treatments reduced the incidence of Striga or Alectra infection compared to 80 and 20kgPha-1K Molybdenum application also reduced the incidence of Striga or Alectra infection compared to the control while combined application of 0.25kgMoh-1 and 40kgPha-1 resulted in the lowest incidence of infection by Striga or Alectra compared to the control. Application of 80kgPha”‘ either alone or in combination with various levels of Mo produced the highest TDM. Compared to Alectra infested but unfertilized plots, application of 80kgPha_1 to Alectra infested plots increased TDM by 77%, the corresponding figure for Striga infested plot being 109%. In respect of Mo fertilization, application of 0.25kgMoha-1 and O.SOkgMoha”1 to Alectra infested plots increased TDM by 33 and 44%, respectively, the corresponding figures for Striga being 30 and 33%. Cowpea grain yield was also increased compared to the control. Phosphorus at 40kg Pha-1 produced the highest grain yield among the P levels. However, among all fertilizer treatments application of Mo at 0.50kgha”‘ and 40kgPha-1 produced the highest grain yield;compared to grain yields of the control, application of these levels of Mo and P resulted in 221% increase in grain yield in Alectra infested plots and 144% increase in Striga infested plots. Application of P enhanced nodulation and nitrogen fixation compared to the control. Application of 40kgPha-1 resulted in higher nodule number, nodule dry weight and percentage N-fixed either alone or in combination with various levels of Mo in the Striga or Alectra infested plots.

COMPETITION FOR NODULE SITES BY COWPEABRADYRH1ZOBIUM AND PARASITIC FLOWERING PLANTS AS AFFECTED BY INOCULATION, N, P AND Mo.