Growth and Yield Performance of Solanum tuberosum Grown from Seed Potatoes Infected with ‘Candidatus Liberibacter solanacearum’ Haplotypes A and B

Zebra chip (ZC) disease of potato (Solanum tuberosum) is associated with infection by ‘Candidatus Liberibacter solanacearum’ (Lso). Two haplotypes of Lso—A and B—occur in the United States. Lso haplotype B is more virulent than haplotype A, causing greater disease incidence in tubers, more severe symptoms, and greater loss in tuber yield. This study assessed whether tubers from infected plants generate new infected plants the following year. The effects of both Lso haplotypes A and B on tuber resprout were examined on five potato cultivars. When compared with noninfected tubers, overall plant emergence rate from Lso A- or B-infected tubers was lower, plants emerged slower, and plants generated lower daughter tuber yields in weight and quantity. Plants generally emerged poorly from Lso B-infected tubers and produced lower daughter tuber yields than Lso A-infected tubers. Regardless of Lso treatment, all daughter tubers were asymptomatic, and only 0.3% tested positive for Lso in experiments conducted over 2 years. This suggests that plants generated from Lso A- and Lso B-infected seed potatoes with severe ZC symptoms are likely not a significant source of Lso in potato fields.

Seed Potato Growth and Yield as Affected by Mother Plant Exposure to Herbicides

In a repeated multi-year study, mother potato plants were exposed to herbicides at rates that simulated off-target application, such as through tank contamination. Following exposure of mother plants to herbicides, seed from mother plants was planted in the following growing season and crop growth, yield and tuber quality were quantified. Visual injury from herbicides was observed both in the mother plant and daughter tuber growing seasons and occasional impacts on tuber yield were noted. However, an inconsistent relationship was observed for herbicide related injury and tuber yield reductions of mother potato plants with daughter tuber growth and yield. The lack of consistency in the relationship between visual potato injury in the mother plant production and adverse daughter tuber growth and yield in the following year challenges traditional crop scouting as a tool to predict off-target herbicide risk near seed potato production.

Morpho-phenological and Antibacterial Characteristics of Aconitum spp.

Aconitum species have been traditionally used as ethnomedicine to cure various ailments. The present study reveals the morpho-phenology and antibacterial property of alkaloid extracts of the two Aconitum species. The morpho-phenological characteristics will be helpful for determining the resource availability. Aconitum nagarum is erect type, whereas, Aconitum elwesii is a climber. Aconitum elwesii grows in advance of A. nagarum in terms of growth, flowering and senescence. Towards the end of the year, when the fruits have ripened, the parent tuber dies off. As a result, the daughter tuber becomes independent and in the following spring, takes over the function of the parent tuber. Aconitum nagarum and A. elwesii were found to contain 4-5 aconitine equivalent (AE) mg/g of alkaloid. These alkaloids showed antibacterial activity against different bacterial species including human pathogens, namely, Staphylococcus aureus, Salmonella typhimurium, Bordetella bronchiseptica, Escherichia coli, Bacillus subtilis, Pseudomonas putida, Pseudomonas fluorescence and Xanthomonas campestris. However, the extent of antibacterial activity varied among different bacterial species. The antibacterial activity against S. aureus, B. bronchiseptica, and B. subtilis was bactericidal in nature, whereas, against other tested bacterial species was bacteriostatic. Efficacy of the antibacterial activity of these alkaloids was evaluated by comparing with that of standard antibiotics. Differential localization of the antibacterial principle was observed among the Aconitum species studied.

Phytotoxicity and Translocation of Glyphosate in the Potato (Solanum tuberosum) Prior to Tuber Initiation

Field and greenhouse experiments were conducted to observe and measure the phytotoxicity of glyphosate [N-(phosphonomethyl)glycine] to potatoes (Solanum tuberosumL. ‘Russet Burbank’) applied at different stages of growth and to determine if glyphosate was translocated into the original mother tuber (seed piece) prior to initiation of daughter tubers. Glyphosate injury symptoms appeared 1 day after treatment and at least 50% of the foliage was necrotic within 7 days. Significant decreases in plant height, shoot and root dry matter content, and daughter tuber production were recorded at the 0.28- and 0.56-kg/ha rates. Higher rates of 1.12 and 2.24 kg/ha did not give further significant reductions. Maximum levels of14C activity accumulated in all plant parts 4 days after application of the14C-glyphosate. The14C-glyphosate accumulated primarily in the apical meristem and roots. Extremely low levels of14C activity were detected in the mother tuber regardless of plant age when treated. Phytotoxic effects on the eyes of the mother tuber increased in severity with increasing rates of glyphosate as evidenced by abnormal sprouting.

Phenology, morphology and reproductive biology of the tuberous sundew, Drosera erythrorhiza Lindl

The seasonal growth cycle of Drosera erythrorhiza was examined in native habitat near Perth, W.A. Vegetative growth was from autumn to late spring (March to October), aestivation by underground tubers from November to February. Each germinating tuber produced an upward growing stem terminated at the soil surface by a rosette of glandular leaves. Light was required to initiate the rosette. New tubers formed during July and August. A positively geotropic axillary shoot (dropper) developed from the stem base and penetrated the epidermal sheath(s) of the parent tuber to form a replacement tuber within the emptying storage tissues of its parent. Diageotropic axillary shoots (rhizomes), produced higher up the stem, extended radially, each swelling terminally to produce a daughter tuber. Plants flowered profusely only after fire, and were not observed to reproduce from seed. Reproduction of clones was analysed in terms of number and depth of placement of parent and daughter tubers. Age structure of clones was studied by counting epidermal sheaths surrounding tubers. Clones appeared to undergo cyclic rejuvenation, periods of intensive daughter tuber production alternating with periods of minimal reproduction. Soil type, fire history and season modified this reproductive behaviour by affecting the intensity of daughter tuber production and the growth and survival of tubers.