c2 -~i Resistance of Some Rex Begonia Cultivars
to Xanthomonas campestris pv. begoniae
AR. Chase '
University of Florida, IFAS qP 3 0 1994
Central Florida Research and Education Center Apopka
CFREC-Apopka Research Report, RH-92-18 University of Florida
Begonias were first found infected with Xanthomonas campestris pv. begoniae in thg.
late 1920's (1). Symptoms can be confined to leaves, stems and petioles or sometimes a
systemic infection results in a wilt. Foliar lesions are initially small, circular, translucent and
expand with age into chlorotic and finally necrotic areas. Infections usually occur through
hydathodes or wounds by bacteria moving in water. Systemic infections apparently result
from invasion of wounded roots (2).
Although removal of symptomatic leaves is sometimes recommended for control of
bacterial diseases, it is not advisable on Rieger Begonias since the pathogen readily becomes
systemic in this host. Removal and destruction of systemically infected plants are warranted
in light of the poor chemical control achieved with the bactericides available today (2, 4).
Reduction of free water on plant foliage will decrease development of new infections of
leaves but may not reduce spread of systemic infections. High fertilizer rates have been
found to decrease severity of Xanthomonas leaf spot and blight of Rex Begonia but the best
rate for disease reduction resulted in stunting, decreased leaf size and marginal burning on
the plant (3).
Xanthomonas campestris pv. begoniae has been found on Rieger Elatior, fibrous,
tuberous, Lorraine Elatior, and Rex Begonias with the most severe problems found on
Riegers. Rieger cultivars are moderately to highly susceptible to this pathogen (5). Since
information on susceptibility of Rex cultivars has not been published, the following study was
undertaken to evaluate the relative susceptibility of eight Rex Begonia cultivars to X.
campestris pv. begoniae.
Liner size plants (3-5 inches tall) were obtained from commercial producers and
established in 4 inch pots containing Vergro potting medium. They were top-dressed with
1.5 g Sierra slow-release fertilizer (17-6-12 with minor elements). Eight cultivars were
included in Test 1: Cleopatra, Dew Drop, Helen Teupel, Marion Louise, Mikado, Phoenix
Red, Red Pride, and Tiger Kitten. Three tests were performed using ten plants each of
these cultivars between 18 October 1990 and 16 June 1992. Two additional tests with seven
other cultivars were performed between 14 January 1991 and 16 June 1992. The following
cultivars were included in Test 2: Duarten, Her Majesty, Meteor, Pauline, Peace, Red Dot,
and Vesuvius. Plants were placed on a mist bench (15 sec mist every 30 min from 0800 to
1Professor of Plant Pathology, Central Florida Research and Education Center Apopka,
2807 Binion Road, Apopka, FL 32703.
2000 hr daily) one day before inoa
evaluated six weeks after inoculal
surface with symptoms of disease.
for significant effects.
Differences between trials
severity with the first trial in each '
Rex Begonia cultivars showed si
campestris pv. begoniae (Figure 1)
Drop, Red Pride, and Phoenix F
susceptibility in Test 1 were Maric
highest disease severity ratings wil
An overall ranking of the fi
1. When all 15 cultivars were c
affected by leaf color, size, shape,
significant differences in susceptibi
grown. Growers should choose cu
begoniae as well as the growth cha
Table 1. Relative susceptib
campestris pv. bego
Highly susceptible M
Dew Drop C1
Phoenix Red Ti
Figure 1. Susceptibility of son
begoniae (Test 1).