Management Of Crown Gall Disease In Selected Rosa Hybrida Farms In Kenya Using Artemisia Annua Leaves And Zingiber Officinale Rhizome Extracts

ABSTRACT

Rose flower is the world’s most traded cut-flower with 74% of it coming from

Kenya. Kenya has potential for higher rose production if challenges of pests and

diseases are dealt with. Pests like spidermites, false codling moth, caterpillars,

aphids, thrips, nematodes and diseases such as crown gall, downy mildew, powdery

mildew and botrytis highly compromise production. Crown gall disease, caused by

Agrobacterium tumefaciens is the most problematic disease of roses in Kenya and

causes a production loss of up to 60% depending on age and variety. This study

evaluated the prevalence of crown gall disease and management of the disease using

Zingiber officinale rhizome and Artemisia annua leaves extracts, in an effort to

replace conventional chemicals due to their environmental and economic cost.

Survey of selected flower farms in Kenyan showed a crown gall prevalence ranging

from 0.1% to 65%. Zingiber officinale and Artemisia annua phytochemical

screening indicated presence of terpenoids, flavonoids, alkaloids, saponins,

glycosides, phenols and tannins. Agrobacterium tumefaciens colonies used in testing

antibacterial effect of the extracts were isolated from crushed crown galls and

purified through their growth in Congo red YEMA medium and yeast peptone

glucose agar. The colonies were authenticated biochemically by Gram staining,

motility test, citrate utilization, catalase production, urease production and

ketolactose test. Antibacterial effect of the extracts were determined by measuring

the diameter of the inhibitory zone around the filter discs soaked in extracts on

Agrobacterium tumefaciens inoculated media. Micro-dilution technique on

microtiter plate was used to determine the minimum inhibitory concentrations of the

plant extracts used in soaking the filter discs. Artemisia annua, Zingiber officinale,

mixture of Zingiber officinale and Artemisia annua had Minimum inhibitory

concentration of 125mg/ml, 62.5mg/ml and 31.25mg/ml respectively. The

recommended rate (6.25 ml/l) of copper hydroxide was used. Copper hydroxide and

Artemisia annua had antibacterial inhibitory zone of 12.8mm. This zone was

significantly different from that of Zingiber officinale and mixture of Zingiber

officinale and Artemisia annua which was 10.6 and 10.2 mm respectively (P ≤0.05).

The research therefore revealed that Artemisia annua and copper hydroxide

inhibited bacterial growth better than Zingiber officinale and mixture of Zingiber

officinale and Artemisia annua. Results of treatments done on inoculated rose plants

in the greenhouse in terms number of plants with galls, gall weight and stem length

showed similar tread to in vitro bacterial growth inhibition. The ultimate stem length

of Artemisia annua and copper hydroxide treatment were 69.4cm and 65.8cm

respectively. These lengths were better and significantly different from that of

Zingiber officinale and mixture of Artemisia annua and Zingiber officinale which

were 48.8cm and 54.4cm respectively (P ≤0.05). From the results of this research,

Artemisia annua and Zingiber officinale extracts are promising biocontrols for

crown gall in roses. Farmers are recommended to continue with integrated crown

gall control methods and pursue plant extracts as an alternative. The performance of

Artemisia annua extracts compared well with that of conventional copper hydroxide and is therefore the better option.