Vivekanandan, K. and G. D. Bandara. Forest Department, Rajamalwatta Road, Battaramulla, Sri Lanka.

Transcription

1 Vivekanandan, K. and G. D. Bandara. Forest Department, Rajamalwatta Road, Battaramulla, Sri Lanka. LEUCAENA SPECIES RESISTANCE TO PSYLLID (H ETERO PSYLLA CUBANA CRAWFORD) IN SRI LANKA Introduction. Giant leucaena was introduced to Sri Lanka about a decade ago and since then it is being widely used for fuelwood, fodder, and organic fertilizer by farmers. Since 1987, however, the leucaena psyllid Heteropsylla cubana (Crawford) has become a serious pest of leucaena species in Sri Lanka and has spread throughout the country. Resistance to the leucaena psyllid has been observed in many places (Sorensson and Brewbaker 1987, Fuh-Jiumi Pan 1987). A trial was established, in collaboration with the International Leucaena Psyllid Trial (LPT) network, by the forest department of Sri Lanka, with the assistance of the Nitrogen Fixing Tree Association (NFTA), Hawaii, to select resistance varieties to this pest. This report provides fifteen-month data on psyllid populations, damage and growth performance of 11 Leucaena species/hybrids used in the trial. Materials and methods. The trial was established on 23 November 1988 at Kumbalpola, Kurunegala, Sri Lanka (7 15 N E) at 80 m elevation. The mean annual precipitation is 1,900-2,540 mm with two dry spells - one in January-February and the other in August. Mean temperature is 25 with a maximum of 28 C and minimum of 22 C. Soils at the trial site are red yellow Podzols soils containing 60-70% sand, 9-20% silt, and 18-21% clay. Soil ph is 6.2. The experimental design was a randomized complete block with three replicates. The following Leucaena species/hybrids were planted in 5 m long, double row plots, with 1 m between rows and 0.25 m between plants within the row (40 trees/plot). The distance between species plots was 2 m. Table 1. Leucaena species/hybrids planted. 1. Leucaena leucocephala K8 2. Leucaena leucocephala K Leucaena pallida K Leucaena hybrid KX1 (K376 x K165) Pal x Div 4N OPF2 5. Leucaena hybrid KX2 (K8 x K376) Leuca x Pal OPF2 6. Leucaena hybrid KX3 (Leu) x K156 (Div) F2 7. Leucaena diversifolia (4n) K Leucaena diversifolia (4n) CPI # Leucaena collinsii 10. Leucaena diversifolia K Leucaena e s c u l e n t a Origin Moyahua, Zacatecas, Mexico Coahuila, Mexico Oaxaca, Mexico Veracruz, Mexico Veracruz, Mexico Gliricidia sepium was also included as one entry. The trial has been managed as hedges for fodder production by cutting trees back after six months of growth to 50 cm above ground level and subsequently cut to 75 cm height every three months. The measurements and data collected: Psyllid count and psyllid damage. Psyllid counts for three stages and damage levels were scored empirically (1-9 rating) as developed by NFTA (Wheeler 1988). Observations were made on a monthly basis on young leaves at the end of the growing stem. A 7 cm length of a completely

2 foliated juvenile leaf comprised one sample. Eight trees were scored for each entry in each replication. Predator counts and identification. The number of predators were scored at the same time as psyllid counts were made. Growth measurements. Height and basal diameter at 15 cm above ground of eight trees for each entry in each replication were measured before cutting. Leaf and stem were separated and weighed separately. A 50 gm sample from each entry was dried and weighed for dry matter conversion. Climatological data and soil characteristics. The soil of the trial site was analyzed before planting for ph and sand, soil, clay, organic matter, N, P, K, Na, Ca and Mg content. Monthly rainfall and maximum and minimum temperature were recorded during the trial period. Results and discussion. Psyllid population, damage, and climate. Psyllid adult and nymph populations for the 11 leucaena species/hybrids during the period of July, 1988 to April, 1990 are given in Tables 1 and 2. The damage rating of the psyllid are shown in Table 3. Rainfall data is included on all tables for comparison of weather data with population level. Significant differences in psyllid tolerance were shown among species, as reflected by damage and psyllid number during all months. Leucaena species/hybrids K156, #46568, and L. collinsii showed less damage than K8, K636, and KX3. Leucaena species such as K376, KX1, KX2, K785, and L. esculenta showed higher tolerance of the psyllid than other entries throughout the trial period. There were also significant differences among varieties in monthly counts of adults, nymphs and eggs (Figures 1 and 2). Psyllid populations and damage increased in July, August, September and in January, February and March. Infestation and damage were very low from October to December which was the main rainy season and again in April to June. This indicates a high correlation between psyllid population and rainfall. Rainfall (mm) July Aug. Sept. Oct. Nov. Dec. Jan. Feb. March April Figure 1. Seasonal variation in psyllid adults number for susceptible (K8, K636) and tolerant (KX1, KX2, K785) leucaena varieties. Figure 2. Seasonal variation of psyllid damage for tolerant (KX1, KX2, K156, K376, K785) and susceptible (K8) leucaena varieties.

3 Table 1. Trial rating means for psyllid adults and monthly rainfall. Species K N o July Aug 1989 Sept Oct Nov Dec Jan 1990 Feb Mar Apr L. leucocephala K L. leucocephala K L. pallida K KX KX KX L. diversifolia K L. diversifolia CPI# L. collinsii L. diversifolia K L. esculenta Table 2. Trial rating means for psyllid nymphs. Species K N o July Aug 1989 Sept Oct Nov Dec Jan 1990 Feb Mar Apr L. leucocephala K L. leucocephala K L. pallida K KX KX KX L. diversifolia K L. diversifolia CPI# L. collinsii L. diversifolia K L. esculenta Table 3. Trial rating means for psyllid damage to Leucaena spp Species K N o July Aug Sept Oct Nov Dec Jan Feb Mar Apr L. leucocephala K L. leucocephala K L. pallida K KX KX KX L. diversifolia K L. diversifolia CPI# L. collinsii L. diversifolia K L. esculenta

4 Table 4. Plant height and diameter. Species K No 05/07/89 27/10/89 25/01/89 25/04/90 L. leucocephala K L. leucocephala K L. pallida K KX KX KX L. diversifolia K L. diversifolia CPI# L. collinsii L. diversifolia K L. esculenta Table 5. Biomass production (leaves and stems) of leucaena species at cuttings (dry weight kg/2 m hedge). Species KNo. 05/07/89 27/10/89 05/01/90 25/04/90 L. leucocephala K L. leucocephala K L. pallida K KX KX KX L. diversifolia K L. diversifolia CPI# L. collinsii L. diversifolia K L. esculenta Plant growth. Heights and stem diameters (15 cm aboveground) of K8, KX2, and KX3 were greater than that of other varieties in the trial (Table 4). There were little difference between remaining varieties. Biomass production. KX1, KX2, and K785 expressed higher tolerance to psyllid than other provenances under the trial and at the same time exhibited faster and more active regrowth after cutting (Table 5). Both K8 and K636 exhibited similar levels of psyllid damage; however, K636 exhibited quick regrowth and recovery from the damage. Predators. During the trial period some psyllid predators were observed, mainly indigenous coccinellid and dragonflies, but their role in controlling psyllid is negligible. Conclusions. The results from these trials confirm that KX1, KX2, and K785 have greater psyllid tolerance and high productivity, and that K636 and KX3 have high productivity despite their low tolerance to the psyllid. The productivity and adaptability to different climatic conditions of these promising species/hybrids needs further testing.

5 Acknowledgements. The authors wish to acknowledge the cooperation of NFTA, Waimanalo, Hawaii, in providing planting materials, advice and other support for the work reported here. References: Sorensson, C.T. and J.L. Brewbaker Psyllid resistance of leucaena hybrids and species. Leucaena Res. Reports 7(2): Pan, Fuh-jiunn Psyllid resistance of Leucaena species in Taiwan. Leucaena Res. Reports 7(2): Wheeler, R A Leucaena psyllid trial at. Leucaena Res. Reports 9:25-29.