Developmental Anatomy of Zucchini Leaves with Squash Silverleaf Disorder caused by the Silverleaf Whitefly

Abstract

<jats:p>Squash silverleaf (SSL) is a physiological disorder of vegetables in the genus <jats:italic>Cucurbita</jats:italic> L. caused by feeding of nymphs of the silverleaf whitefly (SLW) (<jats:italic>Bemisia argentifolii</jats:italic> Bellows &amp; Perring). SSL causes a silvering of the leaves and a blanching of fruit. Leaf silvering is caused by developmental separation of the upper epidermis and the palisade mesophyll layer resulting in additional air space and altered light reflection. The anatomical development of SSL was analyzed in young leaves of zucchini squash (<jats:italic>Cucurbita pepo</jats:italic> L.) using two susceptible genotypes (`Elite' and YSN347-PMR) and two tolerant genotypes (ZUC76-SLR and ZUC33-SLR/PMR). SLW nymphs were allowed to feed only on the mature leaves and the anatomy of the developing leaves was observed by light microscopy and transmission electron microscopy. Silvering began at the apex of young leaves and developed basipetally. The increased percentage of air space that resulted between the upper epidermis and palisade layers was the result of an increase in the duration of air space development in young, developing leaves. Chloroplasts in silvered tissue of mature leaves and in tissue of young leaves that later became silvered, were smaller and contained less starch than chloroplasts in tissue from noninfested plants. In contrast, development of genetic silvering, a condition not related to whitefly feeding, occurred throughout the entire leaf at one time, beginning as yellowed tissue in the axils of leaf veins then turning silver. Chloroplasts were normal in genetically silvered tissue of genotype YSN421-PMR. The SSL-tolerant genotype, ZUC76-SLR, did not show alteration in chloroplast structure or air space development when challenged with SLW; however, it had shorter and paler petioles, as did the susceptible genotypes. SSL symptoms were induced with spraying of gibberellic acid synthesis inhibitor chlormequat chloride in SSL-susceptible but not in SSL-tolerant genotypes. Reciprocal grafting between susceptible and tolerant plants showed that tolerance resides in the developing tissue and not the mature tissue on which the whiteflies feed.</jats:p>

Management of Aphid-Borne Viruses andBemisia argentifolii(Homoptera: Aleyrodidae) in Zucchini Squash by Using Uv Reflective Plastic and Wheat Straw Mulches

“…Virus infection causes a substantial reduction in photosynthesis and an elevation in respiration (Bawden 1964). Silvered leaves contain smaller chloroplasts (Schmalstig and McAuslane 2001) and a reduced chlorophyll level (Yokomi et al 1995). The severity of squash silverleaf seems to be less on plants previously infected with one or more of the viruses.…”

“…Injury occurs by the direct feeding of both adults and immatures. In addition, the nymphs, but not the adults, cause a physiological condition known as silverleaf that leads to a silvering of the leaves and a blanching of the fruit, which renders it unmarketable (Costa et al 1993, Schmalstig andMcAuslane 2001). Whiteßy management using chemicals has not been effective (Denholm et al 1996, Horowitz andIshaaya 1996), and there are few examples of effective biological control in vegetables (Heinz 1996, Hoelmer 1996.…”

Identification of molecular markers associated with resistance to squash silverleaf disorder in summer squash (Cucurbita pepo)

“…It is characterized by prominent silvering of the leaf veins and the adaxial leaf surface caused by the progressive development of large air spaces between the palisade mesophyll cells and the adaxial epidermis (Jimenez et al 1995;Schmalstig and McAuslane 2001). Severely symptomatic plants can exhibit stunting and yield reduction (Jimenez et al 1995;Simons et al 1988).…”

Characterization of Resistance to Squash Silverleaf Disorder in Summer Squash

“…Squash silverleaf (SSL) disorder is an economically important physiological disorder affecting squash (Cucurbita pepo L.) throughout the United States, the Caribbean region, and Israel (Cardoza et al, 1999). It is characterized by silvering of the veins and of the adaxial leaf surface caused by the progressive development of large air spaces between the palisade mesophyll cells and the adaxial epidermis attributable possibly to increased or prolonged cell wall degradation (Jimenez et al, 1995, Schmalstig andMcAuslane, 2001). Silvered leaves exhibit reduced photosynthetic ability possibly as a result of a significant increase in chloroplast disruption and light reflectance (Schmalstig and McAuslane, 2001).…”

“…It is characterized by silvering of the veins and of the adaxial leaf surface caused by the progressive development of large air spaces between the palisade mesophyll cells and the adaxial epidermis attributable possibly to increased or prolonged cell wall degradation (Jimenez et al, 1995, Schmalstig andMcAuslane, 2001). Silvered leaves exhibit reduced photosynthetic ability possibly as a result of a significant increase in chloroplast disruption and light reflectance (Schmalstig and McAuslane, 2001). Severely symptomatic plants can exhibit stunting and fruit yield reduction (Maynard and Cantliffe, 1989;Simons et al, 1988).…”