Epidemiological investigations of black leaf mold (Pseudocercospora fuligena (Roldan) Deighton) on tomato (Solanum lycopersicum L.) under protected cultivation [Elektronische Ressource] / von Zelalem Mersha Ayele

Zelalem Mersha Ayele

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• Publié par: gottfried_wilhelm_leibniz_universitat_hannover
• Publié le: 01 janvier 2008
• Nombre de lectures: 18
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

Epidemiological Investigations of Black Leaf Mold
(Pseudocercospora fuligena (Roldan) Deighton) on Tomato (Solanum
lycopersicum L.) under Protected Cultivation


Der Naturwissenschaftlichen Fakultät
der Gottfried Wilhelm Leibniz Universität Hannover
zur Erlangung des Grades eines


Doktors der Gartenbauwissenschaften
- Dr. rer. hort. -

genehmigte Dissertation

von
Zelalem Mersha Ayele (MSc.)
geboren am 20.10.1972 in Melkawerer, Äthiopien

2008

Epidemiological Investigations of Black Leaf Mold
(Pseudocercospora fuligena (Roldan) Deighton) on Tomato (Solanum
lycopersicum L.) under Protected Cultivation




Der Naturwissenschaftlichen Fakultät
der Gottfried Wilhelm Leibniz Universität Hannover
zur Erlangung des Grades eines


Doktors der Gartenbauwissenschaften
- Dr. rer. hort. -


genehmigte Dissertation


von
Zelalem Mersha Ayele (MSc.)

geboren am 20.10.1972 in Melkawerer, Äthiopien

Angefertigt am
Institut für Pflanzenkrankheiten und Pflanzenschutz

Hannover, Januar 2008


Referent: Prof. Dr. Bernhard Hau
Institut für Pflanzenkrankheiten und Pflanzenschutz
Naturwissenschafliche Fakultät der
Gottfried Wilhelm Leibniz Universität Hannover
Herrenhäuser Straße 2, 30419 Hannover




Koreferent: Prof. Dr. Hartmut Stützel
Institut für Biologische Produktionssysteme
Naturwissenschafliche Fakultät der
Gottfried Wilhelm Leibniz Universität Hannover
Herrenhäuser Straße 2, 30419 Hannover






























Tag der Promotion: 22 Februar, 2008 Abstract i
ABSTRACT

Macroscopic observations of symptoms and signs of the disease as well as isolation, culturing,
inoculation (Koch’s postulate) and microscopic characterizations (morphological and
molecular) of fungal structures from axenic cultures proved Pseudocercospora fuligena to be
the causative agent of black leaf mold (BLM) in Thailand. Macroscopically, the appearance of
indistinct effuse patches on tomato leaves, amphigenous fructification and prolific fuliginous
appearance of sporulating lesions, predominantly on the abaxial side and as infection
progresses on the adaxial side too, were some of the peculiar features of the disease.
Microscopically, the basic fungal structures like conidial dimension and segments (11-128 µm
in length x 3.5–9 µm in width, with up to 12 septations) as well as fascicles of conidiophores
of P. fuligena were observed. Despite its slowness, P. fuligena grew on all the ten artificial
growth media tested but improved growth and sporulation occurred on tomato oatmeal agar
and carrot leaf decoction agar, both supplemented with CaCO . Stomatal penetration and 3
egress of P. fuligena were testified after light and scanning electron microscopy observations
of cleared as well as intact leaves with the staining using aqueous acid fuchsin solution.
Further conidiogenesis studies on cleared and stained leaves indicated prevalence of primary
and secondary infection hyphae and exponential progression of blocked stomatal apertures.
With this background information of the pathogen, further studies on determinants of the
“infection chain” in terms of favorability of temperature (T), wetness duration (WD) and leaf
age (A) were carried out under ambient (AE) and controlled environment (CE) experiments. P.
fuligena under artificial inoculation in CE experiments was highly favored by a temperature of
28°C. Considering the high mean daily T that prevailed under AE experiments in greenhouses
at central Thailand (duration of < 11 h at T ≤ 28°C and of about 17 hours at T ≤ 30°C), P.
fuligena could be assumed to cause the disease even at a T that surpasses the limit of 28°C.
WD of at least 1 day after inoculation (DAI) was found to be a necessity for P. fuligena
infection to take place. In all the tested parameters, young and fully expanded leaves of 3 and
5 weeks age as well as the youngest leaves (1 week old) were more susceptible than leaves of
7 weeks age. Eventually, all these determinant factors, i.e. T, WD and A, influenced the
incubation (IP) and latent (LP) periods. For instance, under CE both the respective IP and LP
were 2.2 to 5 days and 3 to 9.6 days shorter at 28°C than at 24°C. Whereas a respective IP and
LP of 11 to 13 and 12.5 to 18 days were recorded at 28°C from CE experiments, it was even
shorter in one of the AE experiments lasting only 9.2 to 14.0 (IP) and 10.4 to 16.0 (LP) days.
Under natural infection, however, IP extended from an average of 11 to 25 days. Abstract ii
To test the effect of BLM vis-à-vis host growth, four sequential plantings were carried out in
2005. Weekly assessments of BLM incidence (DI) and severity (DS) fitted well to logistic
functions. The sigmoidal shapes suggested that multiple cycles of infection occurred on leaves
of tomato season-long. At times of heavy disease epidemics, a clear effect of reduced host
growth, particularly in terms of healthy leaf area (HLA), was discernible from a comparison of
treatments with (F) and without (NF) fungicide spray. A standardized disease severity (DS*)
proportion of 0.3 from the two peak-epidemics plantings resulted in a 68% loss of HLA when
treatments F and NF were compared. Comparison of healthy leaf area index of healthy plants
(HLAI ) with that of diseased plants in the F (HLAI ) and NF (HLAI ) treatments showed a HP F NF
respective HLAI loss of 11 and 50%. Two applications of the fungicide mancozeb at 4 and 6
weeks after transplanting (WAT) reduced BLM epidemics by 60 to 90%.
Prevalence of such distinction in level of BLM epidemics amongst the plantings of 2005 led
us to widen the area of investigation of the seasonal epidemics in relation to weather and
yield. From the 24 fortnightly and monthly plantings, three BLM peak-epidemic periods were
identified, i.e. August and September 2005 (1) and 2006 (2) and December to January 2005/06
(3). While maximum DS at the last assessment date of non-fungicide sprayed plants of these
stperiods were 0.81, 0.50 and 0.56, the integral variable DS* was 0.30, 0.14 and 0.20 for the 1 ,
nd rd2 and 3 peak-epidemic periods, respectively. Similarly, favorability indices of temperature
(FI ) were 0.90, 0.61 and 0.66 and of relative humidity (FI ) were 0.51, 0.35 and 0.44 for the T RH
peak-epidemic periods 1 to 3, respectively. Actual comparisons of F and NF treatments of
these three peak-epidemic periods resulted in an average of 31.1% marketable yield loss.
2Marketable yield (MY) was negatively but poorly (r = 0.021) correlated with that of DS*.
Integrating maximum plant height (MPH) in the model MY = (a + b ⋅ MPH) ⋅ (1 − c ⋅ DS*) ,
2however, improved the fit (R = 0.35) with high significance all the parameters. The estimated
coefficient of parameter c in the model suggested that a 1% DS* reduced marketable yield by
≈ 1.2%. Interestingly, the actual MY losses from the comparison of the F and NF treatments of
st rdthe 1 and 3 peak-epidemics were close to the prediction of this model.
Besides BLM, early blight (Alternaria solani) occurred during the cool season plantings in
October and November but was only dominant for the first 3 to 6 WAT and taken over by
BLM thereafter. Taking into consideration the shared and overlapping niche of both diseases
TMand that early blight has minor to negligible importance in the BioNet greenhouse, only the
impact of BLM was analyzed in the seasonal dynamic study.
In an effort to pinpoint the source of epidemics and design strategies of BLM management,
the vertical distribution of BLM was studied across the canopy of the tomato cultivar
TMFMTT260 in the BioNet greenhouse. After 16 weeks of a natural epidemic, DS of the lower Abstract iii
canopy layer (0-50 cm) was 42% and significantly higher compared to 26% of the middle (51-
150 cm) and 5% of the upper (> 150 cm) layer. During the growing period of another natural
epidemic, a similar distribution of BLM was observed, but higher DS and bigger lesions were
detected on leaf positions 5 to 10 (in ascending order from bottom up) than on the first four
leaves borne in the nursery. Further non-destructive samplings revealed the earliest BLM
symptoms on leaf positions 5 to 8. When cohorts of 5 leaves were formed starting from the
bottom, BLM incidence of leaves of the 1st cohort was only 79% while the next two cohorts
reached 100%. In artificially inoculated plants, however, BLM was clearly more prevalent in
the middle layer of the plant canopy as compared to the lower and the top part. Plants
inoculated at 4 weeks after transplanting and monitored 10 days later, showed a DS of 43, 67
and 21% on the 1st, 2nd and 3rd cohorts, respectively. Thus, given equal chance of P. fuligena
inoculum to infect all leaves of a tomato plant at one time, more BLM developed on fully
expanded younger leaves than older ones. The high BLM severity of the lower canopy in