Gas chromatography for detection of citrus infestation by fruit fly larvae (Diptera: Tephritidae)

Tephritid fruit flies are serious economic pests worldwide. As larvae, they feed and develop within the pulp of host fruits, making infestation difficult to detect by visual inspection. At U.S. ports of entry, incoming produce shipments are checked for infestation by manually cutting open a small sample of fruit and searching for tephritid larvae. Consequently, there is a need for more sensitive, high-throughput screening methods. This study evaluated gas chromatography (GC) as a potential technology for improved detection of hidden infestation. Grapefruits (Citrus × paradisi Macfad.) infested with immature stages of the Caribbean fruit fly Anastrepha suspensa (Loew) (Diptera: Tephritidae) were examined to determine if infested fruit emitted a chemical profile distinct from that of non-infested fruit. Peaks identified by GC analysis were grouped into three classes. Chemicals detected in similar quantities in all samples, or slightly elevated in infested samples, were regarded as non-diagnostic background volatiles. Chemicals highly elevated after oviposition, during the last instar exit stage, and in experimentally-pierced fruit were interpreted to be indicators of citrus peel injury, and included d-limonene and β-ocimene. Chemicals elevated exclusively in the larval infestation stages were considered indicators of feeding damage and potentially diagnostic of infestation, and included hexyl butanoate and an unidentified compound. The peaks associated with injury and feeding were also detectable with a portable ultra-fast GC analyzer that required less than 80 s per sample. Further studies will investigate the potential application of these results for development of a rapid, non-destructive screening method for detection of tephritid infestation.     

Interactions between mitochondrial lipid oxidation and oxymyoglobin oxidation and the effects of vitamin E

Off-flavor and discoloration of meat products result from lipid oxidation and myoglobin (Mb) oxidation, respectively, and these two processes appear to be interrelated. The objective of this study was to investigate their potential interaction in mitochondria and the effects of mitochondrial alpha-tocopherol concentrations on lipid oxidation and metmyoglobin (MetMb) formation in vitro. The addition of ascorbic acid and ferric chloride (AA-Fe(3+)) increased ovine and bovine mitochondrial lipid oxidation when compared with their controls (p < 0.05); MetMb formation also increased with increased lipid oxidation relative to controls (p < 0.05). Reactions containing Mb and mitochondria with greater alpha-tocopherol concentrations demonstrated less lipid oxidation and MetMb formation than mitochondria with lower alpha-tocopherol concentrations. Greater mitochondrial alpha-tocopherol concentration was also correlated with increased mitochondrial oxygen consumption in vitro and with a more pronounced effect at pH 7.2 than at pH 5.6. Relative to controls, succinate addition to bovine mitochondria resulted in increased concentrations of ubiquinol 10 and alpha-tocopherol and decreased lipid and Mb oxidation (p < 0.05). Mitochondrial lipid oxidation was closely related to MetMb formation; both processes were inhibited by alpha-tocopherol in a concentration-dependent manner.     

Sap flow in ‘Hass’ avocado trees on two clonal rootstocks in relation to xylem anatomy

The rates of sap flow and xylem vessel features were studied in two-year-old nongrafted and grafted avocado (Persea americana Mill.) trees. Daily sap flow rates were measured with heat and balance stem gauges in clonal Duke 7 (D7) and Toro Canyon (TC) trees and ‘Hass’ clonal scions grafted onto clonal D7 (H/D7) and TC (H/TC) rootstocks. Vessel features as size, number and total vessel area were determined histologically in the stem of the scion and rootstock and the roots of the grafted trees. Significant differences in the sap flow rate were found among the rootstocks, where D7 had a 29% higher sap flow rate than did TC (grafted and nongrafted trees). There were no differences among xylem vessel features in the stems of any of the varieties. However in the roots, D7 had wider and fewer vessels then TC do. Also, D7 had a 19% higher total vessel area than TC. These results suggest that the differences in water consumption of ‘Hass’ on different rootstocks may be associated with differences in the efficiency of the roots to absorb water across conductive tissue which may be linked to differences in the area of xylem vessels in the root.