GC–MS of essential oil, metal profile and physicochemical properties of fruits of Citrus macrophylla Wester from Sudan

Background The study investigated the essential oil composition, metal profile and physiochemical properties of Citrus macrophylla Wester fruits collected from Agricultural Research Corporation, Shambat area, Khartoum North, Sudan. The species was introduced by one of the authors Dr. Moawia E. Mohamed from the National Repository of Citrus and Dates of Riverside, California, USA. This species is known as universal rootstock. Results The graphite furnace–atomic absorption spectrometry determined the presence of sodium (6.38 ppm), potassium (701.93 ppm), calcium (371.28 ppm), magnesium (54.78 ppm), cadmium (0.013 ppm), zinc (0.256 ppm) and lead (0.200 ppm). The content of peel, moisture and ash of C. macrophylla was measured as 18.35%, 23.75% and 2.04%, respectively. Among thirty compounds identified using gas chromatography–mass spectrometry, limonene is the major compound (72.85%). The vitamin C (ascorbic acid) content of C. macrophylla juice was determined as 55.0 mg/100 g. The fruit diameter, fruit weight and percentages of juice, peel and seed were determined as 91.4 mm, 276.5 g, 47.92%, 26.37% and 19.20%, respectively. The pH value, total soluble solids (TSS), titratable acidity (TA) and ripening index (RI) of C. macrophylla are found to be 3.50, 8.00%, 7.44% and 10.81, respectively. Conclusion The results in this study suggested that C. macrophylla could be beneficial in food as healthy juice.

Gene Expression under Short-Term Low Temperatures: Preliminary Screening Method to Obtain Tolerant Citrus Rootstocks

Climate change and global warming are leading to a change in weather patterns toward hot and cold waves. Citrus fruits are a tropical or subtropical crop whose growth is altered by changes in weather patterns. Thus, in the present work, two experiments are evaluated to obtain a screening method to select citrus rootstocks that help us to select new low-temperature-tolerant plant materials. One cold experiment was carried out with the Poncirus trifoliata and Citrus macrophylla rootstocks at 4 °C for 4, 8, 24 and 56 h. A second experiment was performed at 4 °C for 5 days with subsequent acclimatization lasting 0, 5, 10 and 24 h. The expression of the cold response genes CAMTA1, CAMTA3, CAMTA5, CBF1, ICE1 and COR413 IM1 was quantified. The results showed that the best rootstock selection strategy was the second experiment, as a higher expression of the genes CAMTA3, CAMTA5, CBF1 and COR413 IM1 was seen in the tolerant genotype P. trifoliata. We quantified the gene expression of proline biosynthesis P5CS1, dOAT and the proline transporters PROT1 and PROT2; the concentration of the amino acid proline in leaves was also quantified. These results once again showed that the best experiment to differentiate between tolerant and sensitive rootstocks was the second experiment with acclimation time.

Feeding and Oviposition Behaviour of Trioza erytreae (Hemiptera: Triozidae) on Different Citrus Rootstock Material Available in Europe

Trioza erytreae (Del Guercio, 1918) (Hemiptera: Triozidae) is a vector of Candidatus Liberibacter spp., the causal agent of Huanglongbing disease (HLB). This study evaluates the preference of T. erytreae in different citrus seedlings. Thus, six different non-grafted citrus rootstocks were used for these experiments: (a) Carrizo citrange; (b) Citrus macrophylla; (c) ‘Cleopatra’ mandarin; (d) Forner-Alcaide No. 5; (e) Forner-Alcaide No. 517, and (f) Poncirus trifoliata (‘Flying Dragon’). The behaviour and survival of this psyllid was evaluated through the feeding preference of T. erytreae adults for different rootstocks (in a choice trial under greenhouse conditions) and oviposition and survival of T. erytreae adults on the different citrus material (in a no-choice trial under laboratory conditions). Trioza erytreae showed a clear preference for hosting and feeding on C. macrophylla, and Carrizo citrange was the most suitable rootstock for insect reproduction and survival followed by C. macrophylla. Conversely, Poncirus trifoliata was the least attractive rootstock to T. erytreae adults in the greenhouse trial and led to significantly lower T. erytreae survival. Our results suggest that conventional citrus rootstocks, such as Carrizo citrange and C. macrophylla, could increase T. erytreae populations.

Substandard and Semi-Dwarfing Citrus Rootstocks for More Intensive, Higher-Density, and Sustainable Plantation Systems

An increasing number of intensive, dense, and sustainable citrus plantations have fostered a growing interest in addressing the future challenges of citrus crops: An increase in the world’s population, climate change, and globalization. Nutrient efficiency and the absence of vigorous citrus rootstocks are required for the success of these plantation systems. The agronomic performances of the “Lane Late” orange cultivar on three substandard or semi-dwarfing citrus rootstocks (Forner-Alcaide no.5 (FA5), Forner-Alcaide no.13 (FA13), and Forner-Alcaide no.41 (FA41)) were evaluated in Spain in comparison with more traditional Mediterranean citrus rootstocks (Carrizo citrange (CA), Citrus macrophylla (MP), and ‘Cleopatra’ mandarin (CL)) under a poor mineral fertilization program over six growing seasons. FA13 and FA41 induced the smallest ‘Lane Late’ trees. Although the rootstock did not induce a significant effect on the ‘Lane Late’ yield efficiency (kg m−3), the highest values were recorded for ‘Lane Late’ on MP, CL and FA13. In this sense, FA13 showed a high productive potential (kg ha−1), given the possibility of narrowing the tree spacing (smaller tree size). Regarding the use of soil nutrients, FA13 was the most efficient citrus rootstock. Thus, FA13 stands out as the most suitable citrus rootstock for more intensive and sustainable plantation systems of the ‘Lane Late’ orange under Mediterranean conditions similar to those of this study.

Quality Parameters of Spanish Lemons with Commercial Interest

The Spanish Mediterranean region concentrates the largest producers of lemons (Citrus limon Burm. f.) at the national level where the 98.4% of the cultivated area of lemons corresponds to the varieties “Verna” and “Fino”. In this study, the morphological and chemical variations of the fruits obtained in five variety/rootstock combinations were investigated in order to determine the influence and impact of the rootstock on the physicochemical properties of the fruits. The assay was carried out using three lemon varieties (“Fino 95”, “Fino 49” and “Verna”) grafted onto two different rootstocks (Citrus macrophylla and Citrus aurantium). The varieties were selected due to be consolidated commercial varieties, while the rootstocks are the most commonly used in the world. Both the morphological characteristics of the fruits (colour, weight, size) as well as their physicochemical characteristics (total soluble solids, titratable acidity, maturity index, antioxidant activity, sugars, and organic acids) were evaluated. Based on the results, the lemons with the best physicochemical and the best compositional characteristics were obtained in the “Fino 95” and “Fino 49” lemons grafted onto C. aurantium rootstock presented the highest quality fruits.

In Vitro Plant Evaluation Trial: Reliability Test of Salinity Assays in Citrus Plants

Salinity is one of the major abiotic stresses affecting crops worldwide, and breeders are urged to evaluate new genotypes to know their degree of tolerance to this selective agent. However, obtaining a number of plants high enough to make the evaluation can prove to be a long and laborious process which could be overcome by using tissue culture techniques. In the present study, the reliability of tissue culture evaluations is called into question through two parallel experiments, in vitro and ex vitro, using Citrus macrophylla and four mutants thereof, previously selected by their different behavior to salinity, as a plant material. Plants were subjected to salinity for 8 weeks in both in vitro (80 mM NaCl) and ex vitro (100 mM NaCl) experiments, and differences with plants grown in control conditions without salt were analyzed. After the experiments, length, leaf damage, shoot dry weight, chlorophylls and ions were measured in both conditions and experiments. As a result, it was demonstrated that tissue culture is a reliable tool to determine whether a genotype is tolerant to salinity or not, since plants of the same genotype responded in a similar way to salinity in both experiments. Henceforth, in vitro evaluations can be employed to test genotypes in a very early stage and using very little time and space. However, genotypes that showed the biggest or lowest changes when cultured in salinity were not always the same in both experiments. Thus, only ex vitro experiments can be performed if the goal is to compare genotypes and see which genotype is the most or least resistant to salinity.

Determination of the Volatile Profile of Lemon Peel Oils as Affected by Rootstock

Citrus limon (L.) Burm is an important crop that grows between latitudes 30° North and 30° South, the main producers being China, the USA, Mexico, India, Brazil, and Spain. In Spain, lemon grows mainly in Mediterranean areas such as Murcia, Valencia, and Andalucía. The most cultivated varieties are “Fino” and “Verna”. In this study, five varieties of lemon, “Verna”, “Bétera”, “Eureka”, “Fino 49”, and “Fino 95” were evaluated on different rootstocks: three new Forner-Alcaide (“FA13”, “FA5”, “FA517”), Citrus macrophylla, Wester, and Citrus aurantium L. Hydrodistillation was used to obtain essential oil from fresh peels and then the volatile profile was studied by gas chromatography-mass spectrometry (GC-MS). A total of 26 volatile compounds were identified, limonene being the main one followed by β-pinene, γ-terpinene, sabinene, and α-pinene. The results revealed that Forner-Alcaide rootstocks (“FA5” > “FA517” > “FA13”) proved to be the best rootstocks for the aroma quality as they led to high volatile contents, followed by C. aurantium and C. macrophylla. Among the other varieties, the most aromatic one was “Eureka”. The whole trend was as follows (in decreasing order): “Eureka” > “Bétera” > “Fino 95” > “Verna” > “Fino 49”.

Feeding Behavior of Asian Citrus Psyllid [Diaphorina citri (Hemiptera: Liviidae)] Nymphs and Adults on Common Weeds Occurring in Cultivated Citrus Described Using Electrical Penetration Graph Recordings

Asian citrus psyllid, Diaphorina citri, transmits Candidatus Liberibacter asiaticus (CLas), the putative causal agent of Huanglongbing disease. Although they primarily feed on the phloem of Citrus and related plants, when grove or host conditions are unfavorable, D. citri may be able to use weed species as alternate food sources for survival. To explore this possibility, electrical penetration graph (EPG) recordings (18 h) were performed to investigate the feeding behavior of psyllid adults and nymphs on three common south Florida weeds (Bidens alba, Eupatorium capillifolium, and Ludwigia octovalvis). EPG recordings revealed that the proportion of time spent by D. citri feeding on xylem was similar on all tested weed species (19%–22%) and on the positive control (20%), the preferred host, Citrus macrophylla. Very little to no phloem feeding was observed on weed species by either nymphs or adults. Histological studies using epifluorescence microscopy showed that salivary sheaths were branched and extended into xylem of weed species, whereas they ended in phloem on citrus plants. No choice behavioral assays showed that adults can obtain some nutrition by feeding on weed species (xylem feeding) and they may be able to survive on them for short intervals, when host conditions are unfavorable.