Subtropical Fruit Crops Research & Education
University of California
Subtropical Fruit Crops Research & Education

Posts Tagged: citrus

Controlling Soil pH with a Grass?

This is an intriguing article that popped up about how to improve blueberry production in alkaline soils.  High pH soils are a major issues for many of our tree crops along the coast.  pH is what controls the availability of most plant nutrients and what bacteria and fungi grow in the soil, creating the biosphere.   So can growing a grass cover crop in our orchards improve lemon and avocado production?

A lawn is better than fertilizer growing healthy blueberries

Intercropping with grasses is an effective and sustainable alternative to chemical treatments for maximizing blueberry yield and antioxidant content in limey soils.


Blueberries are prone to iron deficiency - and correcting it increases their health-enhancing antioxidant content, researchers have discovered.

Published in Frontiers in Plant Science, their study shows that growing grasses alongside blueberry plants corrects signs of iron deficiency, with associated improvements in berry quantity and quality. The effects are comparable to those seen following standard chemical treatment - providing a simpler, safer, cheaper and more sustainable strategy for blueberry farming on sub-optimal soils.

What do superfruits eat?

All soils are rich in iron, but nearly all of it is insoluble.

"Most plants get enough iron by secreting chemicals that make it more soluble," explains senior study author Dr José Covarrubias, Assistant Professor of Agriculture Sciences at the University of Chile. "These iron 'chelators' can be released directly from the roots, or from microbes that grow among them, and allow the iron to be absorbed."

"Blueberries, however, lack these adaptations because they evolved in uncommonly wet, acid conditions which dissolve the iron for them."

As a result, most of the world's relatively dry or alkaline ('limey') cropland is unsuitable for optimal blueberry growth.

"Iron is essential for the formation and function of plant molecules like chlorophyll that allow them to use energy," Covarrubias continues. "That's why iron deficiency shows up as yellowing leaves - and drastically reduces plant growth and yield.

"And in blueberries, iron-dependent enzymes also produce the 'superfruit' antioxidants responsible for their celebrated blue skin and health-enhancing effects."

Strong blueberries must pump iron - but at what cost?

There are two approaches to correcting iron deficiency in blueberries: acidify the soil, or add synthetic iron chelators. Each has its drawbacks, says Covarrubias.

"The commonest industrial approach is soil acidification using sulfur, which is gradually converted by soil bacteria into sulfuric acid. The effects are slow and difficult to adjust - and in waterlogged soils, hydrogen sulfide might accumulate and inhibit root growth.

"Acids can also be added directly via irrigation systems for more rapid acidification - but these are hazardous to farmers, kill beneficial soil microbes, and generate carbon dioxide emissions.

"A commoner strategy among growers is application of iron bound to synthetic chelators - often sold as 'ericaceous fertilizer' - but these are very expensive and leach potentially toxic chemicals into the water table."

A cheaper, safer alternative is needed for efficient large-scale blueberry production. Thankfully, one already exists.

"Grasses - which are well-adapted to poor soils - can provide a sustainable, natural source of iron chelators via their roots when grown alongside fruiting plants. Intercropping with grass species has been shown to improve plant growth and fruit yield in olives, grapes, citrus varieties - and most recently, in blueberries."

A grassroots approach to sustainable blueberry farming

Now, Covarrubias and colleagues have brought intercropping a step closer to the mainstream of blueberry cultivation.

For the first time, they measured the effects of different methods of iron chelation on antioxidant content and other fruit qualities in blueberries.

"In an orchard of 'Emerald' blueberry bushes cultivated in alkaline (pH 8) soil, we compared the effects of five different iron chelation treatments: a 'gold-standard' synthetic iron chelator (Fe-EDDHA), intercropping with grass (common meadow grass or red fescue), cow's blood (Fe-heme), or no treatment (control)."

"We found the association with grasses increased not only the total weight and number of blueberries per plant, but also the concentration of anthocyanins and other antioxidant compounds in their skins, compared to control. The effect sizes were comparable with the proven synthetic chelator Fe-EDDHA, whereas applications of Fe-heme from cow's blood - a fertilizer commonly used in home gardens - had no significant effect."

The beneficial effects paralleled improvement in the plants' iron status (leaf color), which was also comparable between the grass-associated and the Fe-EDDHA-treated plants. None of the treatments had a significant effect on average berry weight

Turf is ready to roll out for healthier blueberries

A potential limitation of intercropping observed in the study was a decrease in berry firmness, since firmer berries are favored by consumers.

"The association with grasses decreased berry firmness compared with control plants, whereas the berries collected from plants treated with Fe-EDDHA reached intermediate values.

"However chemical analysis showed a non-significant trend towards increased ripeness in the berries collected from the intercropped plants, which could account for this small difference."

Intercropped plants also required an additional water supply to maintain a similar soil moisture to other treatments, but plant management was otherwise straightforward and the same across groups. The grasses were kept cropped between 5 and 15cm - a typical range for an attractive mown lawn.

"Our findings validate intercropping with grasses as a simple, effective, sustainable alternative to standard iron correction strategies in blueberries," concludes Covarrubias. "Both commercial and private growers can put this strategy to use right away to boost their blueberry crop and antioxidant content."


Please link to the original research article in your reporting:

Frontiers is an award-winning Open Science platform and leading Open Access scholarly publisher. Our mission is to make research results openly available to the world, thereby accelerating scientific and technological innovation, societal progress and economic growth. We empower scientists with innovative Open Science solutions that radically improve how science is published, evaluated and disseminated to researchers, innovators and the public. Access to research results and data is open, free and customized through Internet Technology, thereby enabling rapid solutions to the critical challenges we face as humanity. For more information, visit and follow @FrontiersIn on Twitter.

soil colors
soil colors

Posted on Tuesday, April 2, 2019 at 11:17 AM
Tags: acid (2), alkaline (2), avocado (272), citrus (304), nutrients (20), pH (6), soil (22)

Citrus Thrips Damage Increase?

A local Ojai grower asks why there seems to be more citrus thrips damage to 'Pixie' mandarins this year.  Was it because of the extended bloom due to warmer spring last year?  The hotter summer up there that was more similar to climate in the Central Valley?  Was it due to the Area-Wide Spraying for Asian Citrus Psyllid - ACP?  Or is this a remnant of the Thomas Fire that dumped ash all over the county, disrupting biocontrol agents like lady bird beetles?

And what else does fire do to citrus?

This is classic  thrips damage. In this area, it is not usually a problem.  This year it seems to be more common. It's not always clear what is the main cause of and what all the interactions are that lead up to an outbreak like this.  Just that there is damage now that occurred 10 months ago.

thrips damage pixie
thrips damage pixie

Posted on Thursday, March 28, 2019 at 2:20 PM
Tags: biocontrol (13), citrus (304), citrus thrips (1), mandarin (65)

How Wierd Can Lemons Get?

In a recent post about lemon shape being affected by high temperatures

a grower sent an image of what I thought was  a blurred view of something that was circled.  I responded saying that I couldn't make it out, and a better image should be sent.

The grower resent the image, but this time it was about the long yellow thing in the background that was being asked about.  The tree is planted next to a chile pepper plant and the question was whether the shape was affected by the chile proximity.

The grower had never seen anything like it before and I haven't either.  But rack it up to the high temperature wave during flowering and the rapid fruit growth period and hormones gone amuck.  if temperature extremes become more common, unusual fruit shapes will likely become more common.


Posted on Friday, March 22, 2019 at 7:43 AM
Tags: citrus (304), climate change (4), hormones (1), lemon (93)

Why is Lemon Sour?

Now we know

A team of researchers, including two from the University of California, Riverside, has identified the genes responsible for the hallmark sour taste of many citrus fruits. Published Tuesday, Feb. 25 in Nature Communications, the research could help plant breeders develop new, sweeter varieties.

Modern citrus varieties have been bred over thousands of years to generate a broad palette of sour and sweet-tasting fruits. Analyses of their pulp reveals that a single chemical element--hydrogen--is largely responsible for the difference between sour and sweet-tasting varieties, which usually have similar sugar content. The pulp from sour fruits contains more hydrogen ions, giving it a lower pH and a tangy taste that is recognized by acid-sensitive cells in our taste buds. Conversely, pulp from sweeter varieties contains fewer hydrogen ions and tastes less acidic.

Ronald Koes and colleagues at the University of Amsterdam in the Netherlands set out to untangle how some citrus varieties wind up with more acidic juice than others, a process that until now has remained a mystery. Their interest stemmed from a previous study showing that higher acidity in purple petunia flowers resulted in more petal pigmentation.

Intrigued by the Faris variety of lemon tree, which produces branches bearing both sweet and sour fruits, and white and purple-tinged flowers, Koes' team turned to UCR plant scientists Mikeal Roose and Claire Federici. Using the university's vast Citrus Variety Collection, which preserves over 1,000 living citrus and related fruit varieties, Roose and Federici selected the Faris lemon and 20 other citrus fruits ranging from wincingly sour to sugary sweet for Koes' team to analyze.

By studying the expression of genes related to those controlling acidity in petunias, Koes' team identified two citrus genes, CitPH1 and CitPH5, that are highly expressed in sour varieties and weakly expressed in sweet-tasting varieties. The CitPH1 and CitPH5 genes encode transporter proteins that pump hydrogen ions into the vacuole, a large storage compartment inside juice cells, thus increasing their overall acidity.

Next, the team turned its attention to genes that control the levels of CitPH1 and CitPH5 in juice cells. While down-regulation of CitPH1 and CitPH5 in sweeter tasting varieties arose multiple times independently in different varieties, the researchers found that mutations in genes for a handful of transcription factors (proteins that help turn specific genes on and off) were responsible for reduced expression of CitPH1 and CitPH5, and therefore a sweeter taste.

Roose, a professor of genetics in UCR's College of Natural and Agricultural Sciences, said the findings could help breeders develop better-tasting citrus fruits. However, he said breeding varieties with severe mutations in the transcription factors such as those studied in the "acidless" citrus would be "overkill," producing sugary citrus fruits with none of their popular acidic kick. Instead, plant scientists should look to target mutations that have a less dramatic effect on the production and activity of transporter proteins.

"By understanding the mechanism acidification of fruit cells, we can now look for related genes that might reduce the expression of CitPH1 and CitPH5 just enough to engineer or select for new, sweeter varieties," Roose said.


Hyperacidification of Citrus fruits by a vacuolar

               proton-pumping P-ATPase complex

Nature Communicationsvolume 10, Article number: 744 (2019)

lemons with some nipples
lemons with some nipples

Posted on Wednesday, March 20, 2019 at 8:41 AM
Tags: acidity (3), citrus (304), lemons (9)

World Citrus News

There's so much gloom about the fate of citrus in Florida and California, but in spite of that talk, world citrus production is increasing.

Global orange production for 2018/19 is forecast to expand 4.2 million tons from the previous year to 51.8 million as favorable weather leads to larger crops in Brazil and the United States. Consequently, fruit for both fresh and processing uses is expected to be greater. Fresh exports are forecast 4 percent higher to 5.1 million tons.

Brazil's production is forecast to rise 13 percent to 17.8 million tons as favorable weather is expected to result in good bloom and fruit set. Fresh orange consumption and exports are flat while oranges for processing are up 2.0 million tons to 12.8 million.

China's production is projected down slightly to 7.2 million on unfavorable weather, resulting in a smaller crop in Jiangxi province. Along with only a small increase in imports, consumption is
lower on overall reduced supplies. South Africa and Egypt are the top two suppliers, accounting for 60 percent of imports.

U.S. production is forecast to recover, jumping 41 percent to 5.0 million tons due to favorable weather. Orange production in Florida has been declining for years due to citrus greening, which has decimated groves and increased costs for crop maintenance.
However, last year, the industry also suffered from damages caused by Hurricane Irma. This year's higher forecast shows a recovery to recent-year levels. Exports, consumption, and fruit for processing are all higher with the larger crop.

Read more about the world citrus industry and get individual country reports generated by the USDA's Foreign Agricultural Service

FAS Reports from Overseas Offices The Citrus: World Markets and Trade circular is based on reports from FAS Overseas Posts since December 2018 and on available secondary information. Individual country reports can be obtained on FAS Online at: .


citrus cornucopia
citrus cornucopia

Posted on Tuesday, March 12, 2019 at 4:25 PM
Tags: citrus (304), lemons (9), markets (4), production (9)

Next 5 stories | Last story

Webmaster Email: