Introduction

Cassava has the ability to adapt to a temporary aberration, low rainfall regions and a permanent feature of climate. Drought originates from a deficiency or irregularity of precipitation over an extended period of time, usually more than a season. Other climatic factors such as high temperatures, high wind, and low relative humidity are often associated with drought. Cassava is a perennial crop which bulking duration ranges from 8 weeks after planting to 24 months after planting which make it a suitable crop for drought prone region of the world. Cassava has a huge yield potential in environments where there is no production constraints, the recorded average annual yield worldwide are 10 ton ha-1 but it can be higher as 90 ton ha-1 been reported in experimental trials of improved cultivars at the International Research Centers. These gaps between the potential and the actual yields on the farmers’ fields are huge and these potentials can be harness (El-Sharkawy, 2005). Therefore, an increase in cassava production in marginal ecology from the use of improved drought tolerant clones will result in increase in global production. A well adapted and poorly adapted clones in these region is necessary for the understanding the genetic and physiological traits that make it a drought tolerant crop. We report drought tolerant and resistant varieties of cassava identified for the maximization of productivity potential in drought-prone agroecology of Sudan Savannah areas of Nigeria.

Materials and methods

Mature stem cuttings was brought from National Root Crops research Institute (NRCRI), Umudike, Nigeria where the initial screen was conducted to select the best adapted and high CMD resistant varieties for different agro-ecologies. The selected field is flat, well-drained with more or less homogenous soil. A simple randomised complete block design (RCBD) of 36 plant plots (6 X 6) and three replications were used. A local variety (Dakata) for the Sudan Savannah region was used as a check to compare the performance of these clones. Measurement of agronomic traits like percentage sprouting, vigour: the plant growth vigour was visually rated using scale of 1-7; Ekanayake et al., 1996, number of primary and secondary stems, primary branching height, primary branching level, Leaves scar number, leaves scar level, number of leaves, leaves area index, and CMD (scale: 1-5), CBB (scale: 1-5) and CGM (scale: 1-5) severity begins at 3 months after planting, all these diseases and pest were observed under natural environmental disease pressure (IITA, 1990). Other traits recorded at harvest are: above-ground biomass, harvest index, storage root fresh weight, number of storage roots, storage root dry matter contents. The plant vigour growth was scored visually with the rate of 1 is where the vigour is very poor, score 3 is where the vigour is intermediate and 5 is very vigorous (Ekanayake et al., 1996). Selection index formula (SI) = [FRY*10]+[DRY*8]+[HI*5]- [CMD*5]-[CBB*8]-[CGM*8]-[PT*3]; weight are allocated according to the importance of each parameter in the dry agro-ecology.

AcknowledgmentsThis work has been partly funded by Alliance for Green Revolution in Africa, National Root Crops Research Institute (NRCRI). We acknowledge the contribution made by Willy Nwakor in the establishment of the trial.

Results and DiscussionThe result obtained shows that different concentration of colchicines influenced the morphology of the cassava varieties used. Table 1 shows that high concentration of colchicines promoted sprouting across the varieties used. The disease status of the materials showed low degree infestation level, each having a disease score of 1 or 2 as shown in Table 2. Table 3, Figures 1a – 1d show the correlation coefficient of the physiological parameters as influenced by the treatment applied. Some of the parameters were positively and significantly influenced while others were negatively influenced. The numbers of leaves were significantly influence with increased level of colchicines and the lengths also increased though not significantly with increasing level of treatment. This means that it is possible to develop cassava varieties with high vegetative cover which provides more photosynthetic surface area as well as provide conducive micro-environment for weed control and others.The length and breadth of leaves reduced with increased level of colchicines showing that colchicines induction can be used to modify the physiology of cassava at will to obtain different population density and varieties for intercropping and maximization of resources.Considering the individual varieties, level 4 gave the highest leave number and highest plant height. Level 2 gave more broad leaves, while increased level of the treatment did not influence the branches.

Table 1. Simple correlation matrix of trait assessed for diseases, agronomic and yield traits in 29 LA and 8 IITA improved genotypes in Sudan savannah of Nigeria in 2010 and 2011 cropping seasons

Clement Adebija1, Olalekan Akinbo2*, Emmanuel Okogbenin2, Chiedozie Egesi2, Favour Ewa2, Eunice Ekaette2 and Martin Fregene3

1Institute of Agricultural Research (IAR), Ahmadu Bello University, Kano Outstation, Kano State, Nigeria; 2National Root Crops Research Institute (NRCRI), Nigeria

3Donald Danforth Plant Centre, 975 North Warson Road, St. Louis, Missouri 63132, USA; corresponding author: akinbooa@yahoo.co.uk

ReferencesEl-Sharkawy MA (2005) How can calibrated research-based models be improved

for use as a tool in identifying genes controlling crop tolerance to environmental stresses in the era of genomics – from an experimentalists's perspective. Photosytnthetica 43:161-176.

Egesi, C.N, F.O. Ogbe, M. Akoroda, P. Ilona and A. Dixon, 2007. Resistance profile of improved cassava germplasm to cassava mosaic disease in Nigeria. Euphytica 155: 215-224.

IITA, 1990

Performance of Screened Latin American genotypes in drought prone Sudan Savannah region of Nigeria

AbstractCassava has been identified as hardy crop that can grow on low nutrient and poor soil with little water. Due to expanding dry agro-ecology and short rain for rain-fed agriculture in dry ecology, early bulking cassava has been recognised as an important character for variety in a drought prone agro-ecology. Five released varieties in Nigeria and 29 genotypes from Latin America germplasm were evaluated in Mijinbir Station, Kano State in Nigeria over three years. Randomized complete block design was used with standard 6 X 6 plot size and a local check (Dakata). In this trial we evaluated for the best early bulking varieties from both the local germplasm from Nigeria and others from the centre of origin. Here we show that AR38-8, CR14B-218, CR52A-1 of Latin America origin have fresh root yield ranges from 20 ton ha-1 to 29 ton ha-1, dry root yield 3.8 ton ha-1 to 5.88 ton ha-1, dry matter content 50% to 61% and harvest index 0.43 to 0.59 in the dry ecology.

Table 2. Mean and ranking by selection index of the yield traits measured from the LA clones evaluated during the 2009 to 2011 cropping seasons

CMD CBB CGM ARCH SCARL RTWT RTNO FRY DRY DMC

CBB 0.82****

CGM 0.79**** 0.90****

ARC 0.05 ns 0.01ns 0.03ns

SCARL -0.05ns -0.01ns 0.05ns -0.2***

RtWt 0.00ns 0.00ns 0.00ns -0.13ns 0.18**

RtNo 0.06ns 0.07ns 0.07ns -0.20ns 0.14ns 0.64****

FRY 0.00ns 0.00ns 0.00ns -0.13ns 0.18* 1.00**** 0.64****

DRY 0.02ns 0.02ns 0.02ns -0.05ns 0.13ns 0.93**** 0.57**** 0.93****

DMC -0.01ns -0.03ns -0.02ns -0.04ns -0.08ns -0.03ns -0.10ns -0.03ns -0.00ns

HI -0.09ns -0.10ns -0.10ns -0.04ns 0.16* -0.50**** -0.27*** -0.50**** -0.44**** 0.01ns

VarietyFRY

(ton ha-1)DRY

(ton ha-1)HI

(0-1)DMC(%)

Ranking by Selection

Index

CW525-1 48.80 26.07 0.55 21.04 117.93 (1)

KNO1 25.21 6.75 0.45 37.34 46.26 (2)

AR9-5 31.05 11.56 0.38 26.00 44.33 (3)

CW450-75 24.33 12.22 0.41 19.68 28.08 (3)

CW451-80 20.07 7.94 0.47 26.46 26.16 (4)

CR14B-180 16.05 5.38 0.45 31.49 19.59 (5)

CR14B-218 13.10 4.81 0.51 27.59 12.84 (6)

CR20A-2 13.60 4.47 0.40 30.37 7.53 (7)

CW450-106 15.05 6.41 0.44 23.47 7.01 (8)

AR14-4 12.57 4.89 0.44 26.48 4.41 (9)

AR9-45 14.75 5.84 0.38 25.79 3.66 (10)

CW451-13 7.00 1.50 0.25 46.45 2.90 (11)

CW450-46 11.15 3.87 0.42 28.77 1.42 (12)

CW450-36 11.54 4.57 0.43 26.11 0.78 (13)

Dakata 9.88 3.22 0.38 30.62 Check

Figure 1. showing yield and disease resistance genotype from the LA clone and the local check during the dry spell and recovery during the rainy season in 2011

Dry spell period

Recovery stage of the LA clone

High yield from LA clone

Local check (yield and disease status)