Abstract:
Alectra Vogelii (Alectra) (parasitic weed) damages cowpea in the semi-arid areas of
Tanzania. Using the petri-dish technique, 14 genotypes from the International Institute of
Tropical Agriculture (IITA), Nigeria and four from Tanzania were assessed for ability to
stimulate the germination of Alectra as a proxy for germination stimulant production using
a completely randomized design (CRD) with 4 replications. Overall 5, 6 and 7 genotypes
were categorised as low, medium and high germination stimulant producer with
germination of Alectra ranging from 16.9-27.5, 27.8-34.0 and 35.4-42.7% respectively.
Genotypes in each category together with 11 ‘no spray’ genotypes also from IITA were
further subjected to Alectra in two sets of pot experiments in a CRD with 4 replications to
investigate the parasitism of cowpea cultivar by Alectra at early growth stages and to
evaluate growth and yield variables. Categorization of cultivars into resistant and
susceptible to Alectra was based on number of tubercles and Alectra shoot length at 5
WAS; days to Alectra emergence, number of emerged Alectra/pot at 9 WAS and grain
yield. All local varieties and 12 IITA’s genotypes were susceptible to Alectra with
tubercles counts/plant ranging from 20.8-45.6 compared to 35.5 in check variety Tumaini,
long Alectra shoots (25.8-38.7mm) compared to 37.8mm in Tumaini. Susceptible cultivars
also had low grain yield (0-1.5g/pot) compared to 0.13g/pot in Tumaini, early emergence
of Alectra shoots (32.3-41.4 days after sowing (DAS) compared to 36 DAS in Tumaini)
and high number of emerged Alectra shoots/pot (55.5-114.4) compared to 80.9 in
Tumaini). For the resistant genotypes IT99K-494-6 and IT98K-205-8 had no Alectra
shoots while IT97K-829-118, IT98K-628, IT99K-7-21-2-2, IT97K-499-35, IT99K-573-2-
1, IT00K-1207, IT97K-568-18, IT98K-131-2, IT99K-573-1-1, IT98K-692 and IT 99K-
530-1 had short Alectra shoots (3.7-15.1 mm). Resistance genotypes also had 35.4-95.7%iii
less number of tubercles/plant compared to Tumaini, high grain yield (2.5-9.1g/pot) and
less number of emerged Alectra shoots/pot by 58.4-99.7% compared to Tumaini.
