Relationships among measurements of fitness and disease severity in Phytophthora infestans

Several methods of estimating pathogen fitness and disease severity in the Phytophthora infestans Solanum tuberosum pathosystem were investigated. Components of fitness measured in a growth chamber were compared with area under the disease progress curve (AUDPC) measured in small field plots. The closest relationship with AUDPC was for sporulation capacity (coefficient of determination, r ²= 0.86)and the least close relationship was with infection frequency ( r ²= 001). Two different methods were compared for calculating the relative fitnesses of two isolates: (i) apparent infection rates and (ii) changes in frequency in mixed epidemics. The values obtained by the two methods were not contradictory (0.98 and 0.93 units per day for the less fit isolate, against 1 for the more fit isolate), but had wide and overlapping confidence intervals.     

The life history of Tenualosa macrura in Sarawak, further notes on protandry in the genus and management strategies

Abstract  The contraction of Tenualosa macrura (Bleeker) to the Sarawak coast and a small part of Sumatra, and the decline in its fishery mirror what has happened to three other species in the genus. Little was known of this species in its last stronghold in Sarawak where it is important for management and conservation reasons to understand its biology and life history. It forms part of a multispecies fishery where effort is uniform, but catches follow a lunar cycle. Tenualosa macrura is protandrous, but low numbers of small females suggest diandry. In Sumatra Tenualosa macrura spawn throughout the year, but in Sarawak have a seasonal peak in the NE monsoon (December). This has management implications because the Sarawak fishery ceases at this time because of adverse weather, hence reducing fishing pressure on spawning T. macrura . Management measures introduced in Sarawak for Tenualosa toli (Valenciennes) may therefore not be required for T. macrura .     

VARIATION OF DENSITY IN THE WOOD OF PINUS PATULA GROWN IN KENYA

1. The specific gravity was determined for the individual ringsof twenty-three 13-year-old stems of Pinus patula grown in Kenyaand also separately on the early and late wood of six rings.
2. Significant correlations were found between specific gravityand both ring width and age ofthe ring from the pith. The effectof ring width was slight with more than six rings to the inch.
3. A comparison with Turnbull's data from South African treesofthe same species confirmed his results only in the firstninerings from the pith.
4. The mean specific gravity of theearly wood in five rings was0.368 compared with 0.469 forthelate wood. This high valuefor the early wood and the smalldifference between early andlate wood was due to the thicknessof the walls in the early-woodtracheids. Similar thickwalledearly-wood tracheids were observedin Kenya species of Juniperusand Podocarpus.

     

Population dynamics and stock status of cobia,Rachycentron canadum,caught in Australian recreational and commercial coastal fisheries

Abstract Age and growth of Rachycentron canadum (L.) was studied in northern and eastern Australia to provide data for a preliminary assessment of the stock and to explore possible fisheries management strategies using minimum legal lengths. Fish collected from commercial and recreational fisheries ranged in size and weight from 125 to 1633 mm fork length (FL) and 0.031 to 55 kg respectively. Annual growth increments in sectioned otoliths formed by November–December. Estimated ages ranged from 0 to 7 yr for both genders. Longevity was estimated to be at least 13 yr. Von Bertalanffy growth function parameters were L = 1160 mm FL, K = 0.63 yr^?1 and t₀ = ?0.21 yr^?1. Rachycentron canadum reach 600 mm FL in their first year and over 1000 mm FL in 3 years. Natural and total mortalities were estimated at 0.35 yr^?1 and 0.85 yr^?1, respectively. Populations of R. canadum may be vulnerable to growth overfishing under the current minimum legal length of 750 mm total length (TL) in Queensland waters. An increase in minimum legal length to 850 mm TL is recommended.