Nursery Trial Research Articles

Fast track evaluation and selection of Hevea brasiliensis clones from a clonal nursery

Ten female parents of natural rubber (Hevea brasiliensis), introduced from two Southeast Asian countries were allowed to natural cross breeding. After a primary culling of seedlings based on growth and test tap yield in juvenile stage, 20 half-sib (HS) progenies were cloned and evaluated in a clonal nursery trial (CNT) laid out (RCBD, plot size 6 with 3 replication) in a close spacing of 2.5m×2.5m. Four established precocious high yielding clones (RRII 430, RRII 414, RRII 105 and PB 235) were included as control. Superior clones were identified based on the important agronomic traits viz., growth, juvenile yield, tolerance to pink disease and bark thickness within a short span of five years, instead of fifteen years in conventional small scale trials (SST) with a wide spacing (4.9m×4.9m). The results indicated that one of the half-sib progeny of mother clone PB 86 (HS PB 86/57) registered significantly (P<0.05) superior dry rubber yield of 18g per tree per tapping (g/t/t), and vigorous trunk girth (43cm) at breast height in the 5th year after planting when compared to that of RRII 105 (11.9g/t/t; 34.1cm girth) and on par with RRII 430 (14.9g/t/t; 31cm girth) and RRII 414 (14g/t/t; 38cm girth), the best among the checks. The second best clone HS LCB 1320/30 also recorded comparable yield and growth with RRII 430 and was better than RRII 414. Three clones (HS PB 86/57, HS BD 5/27 and HS LCB 1320/30) could be selected based on the growth, yield and other secondary traits. None of the trees of HS PB 86/57showed incidence of pink disease and Tapping Panel Dryness (TPD) during field evaluation which deserves attention. The results support superior performance of new genotypes in CNT, saving time and space required to complete the breeding-evaluation cycle. Besides, these clones could be used as improved genetic stocks for initiating new breeding programmes to enrich the genetic base of natural rubber.

Inbreeding depression from selfing and mating between relatives in the Neotropical tree Cariniana legalis Mart. Kuntze

Selfing or mating between related individuals in self-compatible hermaphroditic tree species may lead to inbreeding depression (ID) due to homozygosis in recessive, identical by descent alleles. In general, studies of ID in tree species have been based on comparisons of selfed individuals (produced by controlled pollination) with outcrossed individuals for quantitative traits in progeny tests. However, this approach requires a long time to quantify the extent of ID. Thus, we used an approach based on genetic markers to estimate coancestry coefficients between assigned parents from paternity analysis in two populations of the Neotropical tree Cariniana legalis. Using this method, we were able to determine which seedlings in a nursery trial originated from; (i) outcrossing between un-related trees, (ii) mating between related trees and (iii) selfing. We detected a low selfing rate (<10 %), but a substantial quantity of seedlings from mating between related parents (minimum of 35.7 %). In general, the outcrossed seedlings from unrelated parents exhibited significantly greater genetic diversity than those resulting from selfing and mating among relatives. The extent of ID varied among traits and populations. Outcrossed seedlings originating from unrelated trees generally showed greater survival than seedlings originating from selfing and related parents. Inbreeding depression was greater in the selfed seedlings than in those from mating among related parents. The results are discussed in terms of implications for genetic conservation, breeding and environmental restoration using the species.

Effect of milk replacer program on calf performance and digestion of nutrients in dairy calves to 4 months of age.

Calves fed >0.7kg of dry matter from milk replacer (MR) typically have greater growth preweaning but lower growth postweaning. This is partially explained by lower digestibility of starter due to less development of the rumen at and after weaning; however, it is unclear when digestibility matures postweaning to levels typical of mature ruminants. Thus, we fed Holstein calves (initially 2 to 3d of age) 3 MR programs (MOD=0.66kg daily for 39d, and then 0.33kg daily for 3d, n=15 calves; HIMOD=0.88kg daily for 5d, then 1.1kg daily for 23d, then 0.66kg daily for 18d, and then 0.33kg daily for 3d, n=16 calves; HI=0.88kg daily for 5d, then 1.1kg daily for 37d, and then 0.56kg daily for 7d, n=15 calves). The MR consisted of 28% crude protein and 20% fat and was reconstituted to 14% solids and fed at 0630 and 1400 h daily. A 39% starch textured starter (19% crude protein) was fed free-choice for the first 56d of a nursery trial with calves in individual pens. From 56 to 112d, calves were grouped by MR program into pens of 3 to 4 calves and offered a starter with the same ingredient composition blended with 5% chopped grass hay for ad libitum consumption. Digestion was estimated at 11 and 16wk. Measurements in the first and second 56d were analyzed separately in a completely randomized design using repeated measurements when applicable. Preplanned contrasts of MOD versus HIMOD and MOD versus HI were used to separate means. Milk replacer dry matter intake was 26.6, 42.4, and 48.7kg in calves fed MOD, HIMOD, and HI, respectively. Starter intake was less for calves fed HIMOD and HI versus MOD from 3 to 8wk. Efficiency of metabolizable energy and protein used for body weight gain did not differ among programs. During the second 56d, body weight gain and hip width changes were greater for calves fed MOD than HI. Total 112-d body weight gain and total hip width changes were 101.4, 101.3, and 101.7kg, and 9.0, 9.1, and 8.7cm for MOD, HIMOD, and HI, respectively. Digestibility of all nutrients except starch were greater at 16 versus 11wk of age. Digestibility of dry matter, organic matter, neutral detergent fiber, and acid detergent fiber were less for HI versus MOD at 11wk of age explaining much of the why postweaning body weight gain advantages were lost postweaning in calves fed the HI program. Feeding more than 0.66kg of dry matter intake from a MR during the preweaning phase did not increase total body weight or hip width gain from 0 to 4mo of age.

Potency of tea plant indigenous microbe on plant growth and to against blister blight disease (Exobasidium vexans Massee)

The chemical control method of blister blight (Exobasidium vexans Massee) on tea could inflict various negative impacts. In order to obtain an environmentally sound control method of blister blight disease, a nursery trial has been conducted to know the effectiveness of bacterial combinations. The trial was carried out at Gambung experimental garden, with seven treatments and four replications. The indigenous microbial codes are Azoto II-1, Endo-5 and Endo-76. The treatments tested comprised: control (without bacteria), Azoto II-1 25% + Endo-5 75%; Azoto II-1 50% + Endo-5 50%; Azoto II-1 75% + Endo-5 25%; Azoto II-1 25% + Endo-76 75%; Azoto II-1 50% + Endo-76 50%; and Azoto II-1 75% + Endo-76 25%. All of the treatments was applied as a soil drench, 50 ml/plant with bacterial concentration at 0,5%. The parameter observed was blister blight disease intensity, plant heights, stem diameter, leaves number, root length, and root volume. The results showed that the combination of Azoto II-1 75% + Endo-5 25% could suppress the intensity of blister blight disease with disease intensity 1.27%. The treatments also affected plant heights, stem diameter, leaves number, root length, and root volume, 15.32 cm; 3.38 cm; 8.05 cm; 18.25 cm and 2.37 cm, respectively.

Replacement of fishmeal by vegetable meal mix in the diets ofLitopenaeus vannameireared in low-salinity biofloc system: effect on digestive enzymatic activity

Biofloc (consortium of diverse microorganisms associated to suspending substrates) was developed from waste of shrimp Litopenaeus vannamei postlarvae culture under low salinity (5 g L−1) to provide an additional nutritious biomass and reduce fishmeal inclusion in feeds in a 28-day indoor shrimp nursery trial conducted in 15 experimental containers (250 L stocked at 600 org m−3). Four experimental diets (isoproteic and isocaloric) containing different percentage of fishmeal: 0%, 10%, 20% and 30% substituted by vegetable meal mix (corn, sorghum and wheat) were formulated and elaborated. A control treatment consisted of a commercial feed. The main water quality parameters were monitored, and no significant differences were found among treatments. The growth and survival were similar among treatments. In general, digestive enzymatic activities showed differences being greater in the biofloc system compared with clear water. It was concluded that low-salinity shrimp nursery could be successfully developed with minimum inclusion of fishmeal in feeds, without significant effect on production response. The adjustment of C : N ratio allowed the increase of microbial biomass in the bioflocs, which contributed to maintain good water quality, provide live food and enhance digestive enzymatic activity of cultured organisms.

Evaluation of Bio-inoculants Enriched Marginal Soils as Potting Mixture in Coffee Nursery

Fertile jungle soil is a primary ingredient of potting mixture used in coffee nursery to raise healthy, vigorous seedlings and in recent times its availability has diminished due to the receding forest lands in traditional coffee cultivating areas. Hence a nursery trial was conducted with the objective of exploring the possibility of utilizing marginal or less fertile soils enriched with bio-inoculants in the potting mixture. Two soils, (soil-1 and soil-2), which are less fertile and marginal in characteristics compared to the jungle soil enriched with bio-inoculants consortia of Azosprillum, Pseudomonas flurosence, Phosphate Solubilising Bacteria (PSB) and Vesicular Arbuscular Mycorrihiza (VAM) were employed in the secondary nursery to raise coffee seedlings and monitored for growth parameters, nutrient uptake, soil nutrient status and colony forming units for about 200 days after sowing. The results of the study indicated that the recommended Standard Package of Practice (SPP) with jungle soil, Farm Yard Manure (FYM) and sand in the 6:2:1 proportion is a best suited potting mixture to raise the coffee nursery. But in absence of the fertile jungle soil, the marginal soils also can be utilized as an ingredient of potting mixture with due care to incorporate adequate quantity of farm yard manure and the microbial consortia is not a substitute for FYM in the potting mixture.

Application of arbuscular mycorrhizal fungi with Pseudomonas aeruginosa UPMP3 reduces the development of Ganoderma basal stem rot disease in oil palm seedlings.

The effect of arbuscular mycorrhizal fungi (AMF) in combination with endophytic bacteria (EB) in reducing development of basal stem rot (BSR) disease in oil palm (Elaeis guineensis) was investigated. BSR caused by Ganoderma boninense leads to devastating economic loss and the oil palm industry is struggling to control the disease. The application of two AMF with two EB as biocontrol agents was assessed in the nursery and subsequently, repeated in the field using bait seedlings. Seedlings pre-inoculated with a combination of Glomus intraradices UT126, Glomus clarum BR152B and Pseudomonas aeruginosa UPMP3 significantly reduced disease development measured as the area under disease progression curve (AUDPC) and the epidemic rate (R L) of disease in the nursery. A 20-month field trial using similar treatments evaluated disease development in bait seedlings based on the rotting area/advancement assessed in cross-sections of the seedling base. Data show that application of Glomus intraradices UT126 singly reduced disease development of BSR, but that combination of the two AMF with P. aeruginosa UPMP3 significantly improved biocontrol efficacy in both nursery and fields reducing BSR disease to 57 and 80%, respectively. The successful use of bait seedlings in the natural environment to study BSR development represents a promising alternative to nursery trial testing in the field with shorter temporal assessment.

Evaluation of enhanced nutritional programs for mitigating HLB damage

Florida growers have reported that enhanced nutritional programs (ENPs) maintain productivity of HLB-infected trees.&nbsp; However, efficacy and sustainability of the nutritional approach for HLB disease management remains uncertain.&nbsp; Complementary studies of multiple ENPs and their individual components compared to the standard nutritional program (SNP) on nursery and field trees were initiated in 2010.&nbsp; Two independent nursery trials were initiated with final data collection of the second trial currently underway.&nbsp; The field site was chosen for its mix of healthy, presymptomatic, and HLB symptomatic trees to determine if observed differences resulted from effects on healthy or infected trees.&nbsp; We have found no evidence of reduced phloem plugging in ENP treated nursery trees.&nbsp; Candidatus Liberibacter asiaticus (Las) populations are similar for ENPs and the SNP.&nbsp; Minor differences in Las movement have been observed.&nbsp; Las invaded new flush tissue faster in ENP treated trees than SNP trees.&nbsp; Phosphite treatments have caused Las to favor early invasion of root tissue compared to other treatments.&nbsp; Preliminary observations of the second nursery trial suggest that foliar symptoms are more apparent on the standard nutrient program compared to ENPs; however, root and canopy decline are unaffected.&nbsp; Fruit yield and HLB symptoms in field trees treated with ENPs have not differed significantly from the standard nutritional program after two years.&nbsp; Third year yield data will be presented.

English

Basal stem rot (BSR) disease caused by the fungus, Ganoderma boninense has become a serious threat to the oil palm industry, especially in Southeast Asia (SEA). A highly selective and sensitive diagnostic tool for BSR is extremely required for early detection, and thus, development of immunological test using enzyme-linked immunosorbent assay-polyclonal antibody (ELISA-PAb) was evaluated. Results indicate that ELISA-PAb shows recognition of Ganoderma species associated with BSR except for G. tornatum. Cross-reactivity test with fungi commonly found in oil palm plantation revealed observation of some cross-reactions with some saprophytic fungi. ELISA-PAb shows better detection as compared to cultural-based method, Ganoderma selective medium (GSM) with an improvement of 18% at nursery trial. The present study also demonstrates sensitive detection on ELISA-PAb with an increment of 30% as compared to GSM test at field trial using oil palm roots and stems. Polyclonal antibodies raised against G. boninense with positive signals was achieved, however, not specific enough for detection of BSR disease caused by Ganoderma. &nbsp; Key words: Ganoderma boninense, basal stem rot, polyclonal antibodies, enzyme-linked immunosorbent assay (ELISA).

Fragmentation Genetics of Vateria indica: implications for management of forest genetic resources of an endemic dipterocarp

Tropical agro-forest landscapes are potentially valuable reserves of forest genetic resources for forestry and restoration of degraded forests. The Dipterocarpaceae is a dominant Southeast Asian family of tree species of global significance for the tropical timber industry. Very little information exists about how effective human modified landscapes are for conserving genetic diversity in dipterocarp species. This study provides a baseline for understanding how fragmented agro-forest landscapes in India sustain forest genetic resources in an endemic dipterocarp tree. We compare genetic diversity and fine-scale spatial genetic structure (FSGS) in the threatened tree species Vateria indica within an isolated and a continuous forest site in the Western Ghats, South India. We place these results in the context of dipterocarps from both the Seychelles and Borneo. Parentage analysis of 694 progeny using twelve nuclear microsatellite markers is applied to estimate pollen and seed dispersal. Using a nursery trial we evaluate effects of inbreeding on growth performance. Our results show that levels of FSGS, and gene dispersal are comparable between a small isolated and a large continuous site of V. indica. Realized long-distance pollen flow into the isolated patch appears to help maintaining genetic diversity. The nursery experiment suggests that selection favours outbred progeny. Individuals of V. indica in close proximity appear less related to each other than in another highly fragmented and endangered dipterocarp species from the Seychelles, but more related than in three dipterocarp species studied in continuous forest in Borneo. We discuss the wider implications of our findings in the context of conservation and restoration of dipterocarp forest genetic resources in fragmented populations.

Genetic analysis of poplar (Populus deltoidesBartr.) clones for early generation selection

The study aimed to select the best clones from a field trial of 69 newly developed clones and two check clones of Populus deltoides after 3 years of field performances. Growth traits were assessed for three growing seasons. Significant differences were detected among clones for plant height, stem diameter, estimated trunk volume and sylleptic branch number. Plant height, stem diameter and trunk volume had low to moderate (0.21 to 0.41) broad sense heritability (h2) values. Sylleptic branch number showed high genetic advance (77.53%) despite moderate h2. In nursery trial, the h2 estimates were moderate to high h2 (0.61 to 0.69) for growth traits. It is possible to apply selection on the basis of principal component analysis (PCA) accounting for a large part of the total variance in the observed growth relying on trunk volume followed by stem diameter, plant height and sylleptic branch number. The promising clones viz. FRI-AM-53, -70, -51, -6 and -45 outperformed the control clone G-48. Stem diameter showed high (0.97) genetic correlation with trunk volume and proved to be a reliable criterion for selecting for trunk volume.The set of 25 most promising clones based on PCA1 ranking will be effective for selection of clones at the age of three years.

Advanced evaluation of cowpea (Vigna unguiculata ) accessions for fodder production in the central rift valley of Ethiopia

The experiment was conducted at Adami Tulu Research Center in 2004 with 37 selected lines of grain type cowpea (Vignia species) germ-plasm introduced from Melkassa Agricultural Research Center, Lowland Pulse Improvement Program for the advanced nursery trial. Dolichos lablab (Lablab purpureius both var. Highworth and Rongai) and cowpea (Vignia ungiculata var. white worder training type) were included as a control for herbage yield and quality evaluation and ranking. The top ten accessions of cowpea (IT82D 889, TUX 1948-01F, TVU 1142 4, IT85F 2687, 82D 504-4, IT84D-448, IT93K2046-2, IT87D 551-1, IITAUK91-12, 87D -1802,) and Dolichos lablab var. Rongai was selected using the visual observation data taken during the 2004 growing season and promoted for further advanced evaluation. Advanced evaluation was carried out during the growth period, 2005 and 2006, using randomized complete block design (RCBD) of three replication of plot size 3 × 2 m. Fresh weight yield, hay yield, grain yield of both years showed statistically significant difference among accessions (p<0.005) during both growing periods. There was statistically significant difference in percentage dry matter (DM%), percentage organic matter (OM%), percentage ash (ASH%) and percentage crude protein (CP%) (P<0.0001) and the highest value of 88.94, 79.32, 12.09 and 22.3% were shown by accessions IITAUK91-12, IT87D 551-1, 87D -1802 and IT93K 2046-2, respectively. The different accessions responded to the different seasons differently based on the rainfall duration in their herbage and grain yield that needs further categorization. Key words: Adami Tulu, Dolichos lablab, herbage var. Rongai yield.

Effect of potting media and watering frequencies on the growth of pepper fruit (Dennetia tripetala) seedlings

A nursery trial was conducted in the screen house of the Teaching and Research Farm, Faculty of Agriculture, University of Benin, Benin City, Nigeria in 2011 to investigate the effect of different potting media and watering frequencies on the growth of Dennetia tripetala seedlings. Threedifferent growing media: Rice husks (Rh), pig dung (Pd) and cocoa husk (Ch) were used as sources of growth. They were combined in a 1:1 ratio to make seven media combinations with four watering frequencies at once daily (D1), twice daily (D2), once every other day (D3) and twice everyother day (D4). The trial was laid out in a 7 x 4 factorial design fitted into a Completely Randomized Design (CRD) with three replications. Data were collected on plant height, leaf number, and canopy diameter, stem girth, dry weight of root and shoot. Results obtained revealed that potting medium with sole pig dung significantly produced the best seedling attributes in terms of plant height (11.46cm), stem girth (1.01cm), canopy diameter (9.58cm) while, leaf number (11.16), dry weight of shoots (0.51g) and roots (0.19g) were best with sole rice husk and rice husk plus pig dung (1:1) respectively. Watering twice every other day had a significant (p&lt;0.05) influence on plant height, canopy diameter, stem girth and root dry matter. There were significant interaction effects between sole pig dung and watering once, twice daily and twice every other. However, in order to save labour, money and time spent in watering, watering twice every other day plus pig dung sole may be adequate for raising D. tripelata seedlings.Keywords: Dennetia tripelata, potting media, watering frequency, seedling growth

Characterization of Bioflocs in a No Water Exchange Super-intensive System for the Production of Food Size Pacific White Shrimp &lt;i&gt;Litopenaeus vannamei&lt;/i&gt;

Zero exchange super-intensive recirculating aquaculture systems (RAS) represent an environmentally “friendly” alternative to traditional shrimp culture methods, however the susceptibility to pathogens typically increases as the density of cultured organisms increases. The study describes a greenhouse-enclosed super-intensive RAS, utilizing culture water from a 62-day nursery trial, to grow juvenile (0.99 g) Litopenaeus vannamei , Pacific White Shrimp, to market-size under high stocking density (450/m 3 ). The study evaluated the effects of foam fractionation and settling tank particulate control methods on water quality and microbial particulate related flora in four 40 m3 tanks with two replicates per control method under no water exchange. Microbial communities were distinguished at the gram-stain level using flow cytometric fluorescent activated cell sorter (FACS) methods. Differentiation between all other populations of organisms and particles between 1~20 m m was based upon autofluorescence and forward scatter (a size indicative light parameter) using FACS. Analysis of variance indicated that the microbial communities associated with each particulate control method did not deviate from one another significantly (p>0.05). Gram-positive bacteria were the dominate fraction regardless of particulate control method (p<0.05). Six unique autofluorescence signals were consistently present within each RAS. This study is a first step in using flow cytometry as a tool to document changes in microbial communities in no water exchange super-intensive system for production of marketable shrimp. Shrimp yield and survival was high: 9.34~9.75 kg/m 3 and 94.5%~96.9%, respectively. Further, the data suggest that the use of pre-conditioned water may help to prevent ammonia and nitrite overload and decrease pathogenic organism prevalence.

Evaluation of Trichoderma harzianum strain T22 as biological control agent of Calonectria pauciramosa

The objective of this research was to evaluate Trichoderma harzianum strain T22 as a biocontrol agent of collar and root rot caused by different Calonectria pauciramosa isolates. Thus, the microsclerotia-forming ability and virulence of twenty C. pauciramosa isolates were assessed. Microsclerotia production varied partially among the isolates and dual culture with T22 on carnation leaf agar revealed isolates with both high and low microsclerotia-forming ability. Inoculation tests on red clover (Triflolium pratense) demonstrated its susceptibility to the pathogen. On red clover, the degree of virulence and T22 effects in controlling infections were highly variable among the isolates tested. A nursery trial performed on Feijoa sellowiana seedlings confirmed previous results, clearly indicating virulence variability among C. pauciramosa isolates. For three isolates tested in nursery trial, T22 effectiveness in controlling infection was inversely related to their degree of virulence. Overall, T. harzianum strain T22 showed good antagonist activity in reducing microsclerotia production on carnation leaf and the incidence and severity of collar and root rot on both selected hosts. This data could be crucial in developing integrated pest management strategies in ornamental plant nurseries.

Genetic Improvement in Winter Wheat Yields in the Great Plains of North America, 1959–2008

ABSTRACTData from USDA‐coordinated winter wheat (Triticum aestivum L.) regional performance nurseries collected over the time period 1959 to 2008 were used to estimate genetic gain (loss) in grain yield, grain volume weight, days to heading, and plant height in winter wheats adapted to the Great Plains of North America. In both the Southern Regional (SRPN) and Northern Regional Performance Nurseries (NRPN), linear regression revealed significant positive relationships between relative grain yields of advanced breeding lines and calendar year of the nursery trial. The estimated genetic gain in grain yield potential since 1959 was approximately 1.1% (of the control cultivar Kharkof) yr−1 for all entries in the SRPN, and 1.3% yr−1 if only the most productive entry was considered. For the NRPN, the estimates of genetic gain in grain yield were 0.79% yr−1 for all entries, and also 0.79% yr−1 for the most productive entry. Linear regressions of relative grain yields vs. year over the time period 1984 to 2008, however, showed no statistically significant trend in the SRPN. For the same time period in the NRPN, a statistically significant positive slope of 0.83 was observed, though the coefficient of determination (R2) was only 0.28. Relative grain yields of Great Plains hard winter wheats may have peaked in the early to mid‐1990s, and further improvement in the genetic potential for grain yield awaits some new technological or biological advance.

Use of remediated soil materials for sustainable plant growth

Greenspace is increasingly recognized as a cost-effective end use for brownfield and contaminated sites. These sites are often unsuitable for vegetation establishment, either due to the presence of contaminants, or because the soil is of insufficient quality to support plant growth. The remediation of contaminated sites may also result in a material that is incapable of sustaining vegetation. This paper details the results of a nursery trial to assess the potential of combining a number of soils from contaminated and remediated sites with different amounts of greenwaste compost, in order to establish vegetation. Trials were conducted with grasses, alder (Alnus cordata) and poplar (Populus trichocarpa) over two growing seasons, and the effectiveness of the soil/compost combination was evaluated by soil and plant nutrient analyses and plant growth response. The addition of compost increased the concentrations of P, K, and Mg in soil and leaf tissue, and generally increased the survival, growth and biomass of the grass and trees established in the soils. There was very little improved response from doubling the compost incorporation rate, except for a soil contaminated with hydrocarbons and its thermally remediated counterpart. The study demonstrates that vegetation can be established on remediated materials combined with an appropriate level of compost addition, thus potentially removing a significant portion of contaminated soil from the waste stream. © 2010 EPP Publications Ltd.

Advances in intensifying the cultivation of the shrimp Litopenaeus vannamei in floating cages

Shrimp farming in floating cages has advantages over conventional cultivation systems and is a potential production alternative for low-income communities. We present advances in intensifying the cultivation of L. vannamei in floating cages by testing high stocking densities and a large cage-size not previously used, and introducing partial harvesting for the management of the high shrimp biomass. A 38-day nursery trial made during 2006, using 9-m 2cages showed that the final weight of shrimp and specific growth rate (SGR) were significantly ( P < 0.05) greater when postlarvae was stocked at 950 and 1300 PL/m 2, rather than at 1600 PL/m 2. However, the highest number of juveniles per cage was obtained when the later stocking density was used. A 62-day grow-out trial in 2006, using 9-m 2 cages, resulted in a significantly lower growth rate (0.17 g/day) when juveniles were stocked at 300/m 2, as compared to 0.18 and 0.18 g/day obtained at 200 and 250/m 2. The final shrimp biomass varied significantly among densities and ranged from 1.9 to 2.6 kg/m 2. There were no significant differences in final weight (11.3–12.0 g), survival (77% to 81%), and feed conversion ratio (FCR) (0.84–0.93). A 58-day grow-out trial in 2006 using 200-m 2 cages showed that the final weight and growth rate were significantly greater (17.7 g and 0.27 g/day) when juveniles were stocked at 45/m 2, as compared to 13.3 g and 0.20 g/day obtained at 180/m 2. This density did produce the highest biomass yield (1.9 kg/m 2). A nursery trial was made during 2008, stocking at 1500 PL/m 2 and obtaining results that were consistent with those from the trial of 2006. A 93-day grow-out trial was made during 2008 stocked with 420 and 560 juveniles/m 2 in 9-m 2cages. A partial harvest was made after 62 days when shrimp weighed 8.9 to 9.5 g. A significantly higher biomass yield (1.5 kg/m 2) was obtained at the higher density when compared to 1.2 g/m 2 harvested from the lower density. After the final harvest, the weight of shrimp differed significantly between the lower (14.4 g) and higher (13.2 g) densities, and the corresponding total biomass yields were 4.4 and 5.0 kg/m 2. The values of the zootechnical variables were acceptable when compared to those reported for shrimp cultivation in floating cages, intensive ponds, or raceways, thus indicating the feasibility of further intensifying the cultivation of L. vannamei in cages.

Classification and Inheritance of Morphological and Agronomic Characteristics in Kentucky Bluegrass (Poa pratensis L.)

The apomictic breeding behavior of Kentucky bluegrass (Poa pratensis L.) results in many unique cultivars. A classification system was previously developed to characterize the large number of Kentucky bluegrass cultivars into different types. However, many new cultivars have been released since the last refinement of the classification system. The objectives of this study were to determine differences in morphological and agronomic characteristics among select Kentucky bluegrass cultivars representing the major classification types and to determine broad-sense heritability estimates for important morphological (plant height, panicle length, flag leaf height, and flag leaf length and width) and agronomic (rhizome spread) traits in Kentucky bluegrass. A spaced-plant nursery trial was established in the spring of 2003 at Adelphia, NJ. One hundred seventy-three cultivars and selections were planted in a randomized complete block design with three replications. The morphological and agronomic traits listed were measured on spaced plants. High Density type cultivars (formerly the Aggressive type cultivars) had the most prostrate growth habit with plant heights of 33 and 43 cm in 2004 and 2005, respectively. Mid-Atlantic and Texas × Kentucky bluegrass hybrids had the widest rhizome spread (Mid-Atlantic = 73 and 121 cm; Texas × Kentucky bluegrass hybrids = 72 and 122 cm) in 2004 and 2005, respectively. Broad-sense heritability estimates were high for plant height (H = 0.84), panicle length (H = 0.88), flag leaf height (H = 0.85), and rhizome spread (H = 0.85); moderate for flag leaf length (H = 0.71); and low for flag leaf width (H = 0.11). This study characterizes new cultivars into respective groups and identifies the genetic inheritance of important morphological and agronomic traits in Kentucky bluegrass.

Effect of Rice Sowing Date on Occurrence of Small Brown Planthopper and Epidemics of Planthopper-Transmitted Rice Stripe Viral Disease

To understand the relationship between rice sowing date and occurrence of the rice small brown planthopper (SBPH) Laodelphax striatellus Fallen and the epidemics of the planthopper-transmitted rice stripe viral (RSV) disease, four sowing dates of rice were evaluated in 2006 and 2007. The results showed that the peak density of SBPH and RSV incidence in the nursery and in the transplanted field decreased with the delay of sowing date in single crop of japonica rice in north Zhejiang Province of China. The relationship between seedling RSV incidence at the end of the nursery trial with sowing date was well described by Weibull equation. The area under the curve of population dynamics (AUCPD or planthopper-day accumulation) or the peak density of the planthopper in the nursery could be summarized by a logistic equation. RSV incidence in the transplanted fields could be characterized quantitatively by a multivariate regression equation, including the variables of sowing date, peak density of the vector, and RSV incidence at the end of the nursery trial. That the descriptive model excluded the AUCPD in transplanted field implies that this variable is not necessary in forecasting disease epidemics in the field. The 2-year experiments sufficiently indicated that suitable sowing of rice could be used as one of the effective measures to control the vector population and therefore the planthopper-transmitted RSV on a larger scale. The optimal sowing date for the single-cropped transplanted japonica rice is recommended from late May to early June in north Zhejiang, China.