Development Of A Novel Dna Isolation Protocol And Determination Of The Transmission Mode Of Banana Streak Virus By Putative Vectors In Kisii

ABSTRACT

Banana is an important crop in East Africa. In the tropics, banana and plantains are a major

source of carbohydrate for about 400 million people of whom 200 million are from East

Africa. In Kenya, the banana serves both as a subsistence crop as well as a cash crop. The

production of banana in Kenya is however constrained by viral diseases especially the

Banana Streak Disease (BSD) which is caused by the Banana Streak Virus (BSV). Breeding

between A and B-genomes containing banana have been significantly constrained by BSV

due to activation of the integrated viral sequences in the genome of the interspecific hybrids.

The episomal DNA viral particles are thought to be transmitted by several mealy-bug species

but there are no reports on the transmission of the BSV by other viral insect vectors. This

study aimed at elucidating the mode of transmission of BSV by mealy-bug species in Kenya

and identifying any other putative vectors of BSV in samples collected from infected banana

plantations. The mealy-bugs were reared on pumpkin fruits in black cages and were used in

the virus transmission cycle experiments. The instars of the Paracoccus burnerae (mealybug)

species were fed on BSV infected plants to acquire the virus and on the healthy plantlets

for inoculation. The effect of the acquisition period on the transmission of the BSV, the latent

period and the retention period of the BSV by the mealy-bug species were determined using

Rolling Circle Amplification (RCA). In addition, leafhoppers and banana aphids collected

from the infected banana plantations were assayed for the presence of BSV using RCA. RCA

products were assayed by electrophoretic analysis. Principal characteristics of the modes of

virus transmission by insects were used to conclude the mode of transmission of the BSV by

mealy-bugs. Results from this study revealed that the P. burnerae is able to acquire the virus

and transmit it after a minimum of six hours of acquisition access time. The virus had no

latent period in the vector though it could be retained in the vector for four days after

acquisition feeding, characteristics of semi-persistent mode of transmission. In addition, the

results revealed that Banana aphids and leafhoppers are not potential vectors of BSV.

Viruliferous mealy-bugs should be reduced by destroying BSV infected materials. Greater

understanding of the transmission of BSV will contributed immensely to the development of control strategies for banana streak disease